Print import error when plugin import fails

[maarcingebala]

When a plugin uses a Python package that is not yet installed in the environment, the function that imports plugins would catch the original import error and print a generic message "Plugin doesn't exist" which is confusing. This PR changes this behavior to print the original import error.

Before:

ERRORS:
?: Plugin with path: saleor.payment.gateways.authorize_net.plugin.AuthorizeNetGatewayPlugin doesn't exist

After:

ERRORS:
?: Failed to import plugin saleor.payment.gateways.authorize_net.plugin.AuthorizeNetGatewayPlugin: No module named 'authorizenet'

Impact

• New migrations
• New/Updated API fields or mutations
• Deprecated API fields or mutations
• Removed API types, fields, or mutations
• Documentation needs to be updated

Pull Request Checklist

• Privileged queries and mutations are guarded by proper permission checks
• Database queries are optimized and the number of queries is constant
• Database migration files are up to date
• The changes are tested
• GraphQL schema and type definitions are up to date
• Changes are mentioned in the changelog

[db-queries]

Here is the report for 0c63351 (mirumee:fix-plugin-import-error-message)
Base comparison is cd6ea4e.

No differences were found.

# saleor.graphql.accountbenchmark account
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  delete staff members                                       	         32	         32	              0
  query staff user                                           	         20	         20	              4
  staff create                                               	         22	         22	              4
  staff update groups and permissions                        	         33	         33	              5

# saleor.graphql.accountbenchmark permission group
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  permission group create                                    	         19	         19	              2
  permission group delete                                    	         20	         20	              3
  permission group query                                     	          7	          7	              0
  permission group update                                    	         33	         33	              1
  permission group update remove users with manage staff     	         27	         27	              3

# saleor.graphql.attributebenchmark attribute
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  query attribute                                            	          7	          7	              2
  query attributes                                           	         11	         11	              3

# saleor.graphql.checkoutbenchmark checkout mutations
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  add billing address to checkout                            	         53	         53	              8
  add shipping to checkout                                   	         64	         64	             12
  checkout email update                                      	         26	         26	              3
  checkout payment charge                                    	         34	         34	             11
  checkout shipping address update                           	         64	         64	             13
  checkout voucher code                                      	         64	         64	             10
  complete checkout                                          	        109	        109	             20
  create checkout                                            	         79	         79	             16
  customer complete checkout                                 	        146	        146	             34
  update checkout lines                                      	         91	         91	             24

# saleor.graphql.checkoutbenchmark homepage
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  user checkout details                                      	         39	         39	              2

# saleor.graphql.discountbenchmark sales
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  sales query with channel slug                              	         16	         16	              0
  sales query withot channel slug                            	         15	         15	              0

# saleor.graphql.discountbenchmark vouchers
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  vouchers query with channel slug                           	         16	         16	              0
  vouchers query withot channel slug                         	         15	         15	              0

# saleor.graphql.menubenchmark homepage
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  retrieve main menu                                         	          5	          5	              0
  retrieve secondary menu                                    	          5	          5	              0

# saleor.graphql.orderbenchmark order
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  user order details                                         	         20	         20	              1

# saleor.graphql.pagebenchmark page type
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  query page type                                            	         17	         17	              5
  query page types                                           	         19	         19	              5

# saleor.graphql.productbenchmark category
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  category view                                              	         22	         22	              1

# saleor.graphql.productbenchmark collection
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  collection view                                            	          5	          5	              0
  retrieve collection channel listings                       	          4	          4	              0

# saleor.graphql.productbenchmark homepage
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  report product sales                                       	         10	         10	              3
  retrieve product list                                      	          4	          4	              0

# saleor.graphql.productbenchmark product
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  product details                                            	         24	         24	              0
  retrieve channel listings                                  	         16	         16	              0
  retrieve product attributes                                	          7	          7	              0
  retrive products with product types and attributes         	          5	          5	              0

# saleor.graphql.productbenchmark variant
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  product variant bulk create                                	         59	         59	              2
  retrieve variant list                                      	         22	         22	              2

# saleor.graphql.productbenchmark variant stocks
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  product variants stocks create                             	         22	         22	              5
  product variants stocks delete                             	         19	         19	              5
  product variants stocks update                             	         27	         27	              5

# saleor.graphql.producttest product sorting attributes
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  sort product not having attribute data                     	         23	         23	              0

# saleor.graphql.shippingbenchmark shipping methods
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  vouchers query with channel slug                           	         10	         10	              0
  vouchers query without channel slug                        	          9	          9	              0

# saleor.graphql.shopbenchmark homepage
  test name                                                  	left count 	right count	duplicate count
  -----------------------------------------------------------	-----------	-----------	---------------
  retrieve shop                                              	          2	          2	              0

[codecov]

Codecov Report

Merging #6748 (0c63351) into master (842e7fa) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #6748      +/-   ##
==========================================
+ Coverage   92.75%   92.76%   +0.01%     
==========================================
  Files         397      397              
  Lines       27288    27288              
  Branches     2863     2863              
==========================================
+ Hits        25311    25315       +4     
+ Misses       1389     1385       -4     
  Partials      588      588              

Impacted Files	Coverage Δ
saleor/plugins/checks.py	94.28% <100.00%> (ø)
...aleor/payment/gateways/dummy_credit_card/plugin.py	92.45% <0.00%> (+7.54%)	⬆️

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