INTMDB-242: Fixes the bug when if you don set public/private key it would fail for getting realm client

[coderGo93]

Description

Fixes a bug when if you don't set a public/private key, if you terraform plan with provider mongodbatlas downloaded, it would fail because of bad challenge, it happens because it tries to get a token with empty public/private keys

Results of Acceptance Tests

Resource

make testacc TESTARGS='-run=TestAccResourceMongoDBAtlasEventTrigger'           
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... | grep -v /integration-testing) -v -parallel 20 -run=TestAccResourceMongoDBAtlasEventTrigger -timeout 300m -cover -ldflags="-s -w -X 'github.com/mongodb/terraform-provider-mongodbatlas/version.ProviderVersion=acc'"
?       github.com/mongodb/terraform-provider-mongodbatlas      [no test files]
=== RUN   TestAccResourceMongoDBAtlasEventTriggerDatabase_basic
=== PAUSE TestAccResourceMongoDBAtlasEventTriggerDatabase_basic
=== RUN   TestAccResourceMongoDBAtlasEventTriggerDatabase_eventProccesor
=== PAUSE TestAccResourceMongoDBAtlasEventTriggerDatabase_eventProccesor
=== RUN   TestAccResourceMongoDBAtlasEventTriggerAuth_basic
=== PAUSE TestAccResourceMongoDBAtlasEventTriggerAuth_basic
=== RUN   TestAccResourceMongoDBAtlasEventTriggerAuth_eventProcessor
=== PAUSE TestAccResourceMongoDBAtlasEventTriggerAuth_eventProcessor
=== RUN   TestAccResourceMongoDBAtlasEventTriggerSchedule_basic
=== PAUSE TestAccResourceMongoDBAtlasEventTriggerSchedule_basic
=== RUN   TestAccResourceMongoDBAtlasEventTriggerSchedule_eventProcessor
=== PAUSE TestAccResourceMongoDBAtlasEventTriggerSchedule_eventProcessor
=== CONT  TestAccResourceMongoDBAtlasEventTriggerDatabase_basic
=== CONT  TestAccResourceMongoDBAtlasEventTriggerSchedule_basic
=== CONT  TestAccResourceMongoDBAtlasEventTriggerAuth_basic
=== CONT  TestAccResourceMongoDBAtlasEventTriggerAuth_eventProcessor
=== CONT  TestAccResourceMongoDBAtlasEventTriggerSchedule_eventProcessor
=== CONT  TestAccResourceMongoDBAtlasEventTriggerDatabase_eventProccesor
--- PASS: TestAccResourceMongoDBAtlasEventTriggerDatabase_eventProccesor (39.07s)
--- PASS: TestAccResourceMongoDBAtlasEventTriggerDatabase_basic (39.13s)
--- PASS: TestAccResourceMongoDBAtlasEventTriggerAuth_basic (39.31s)
--- PASS: TestAccResourceMongoDBAtlasEventTriggerSchedule_eventProcessor (39.34s)
--- PASS: TestAccResourceMongoDBAtlasEventTriggerSchedule_basic (39.40s)
--- PASS: TestAccResourceMongoDBAtlasEventTriggerAuth_eventProcessor (40.24s)
PASS
coverage: 5.7% of statements
ok      github.com/mongodb/terraform-provider-mongodbatlas/mongodbatlas 40.587s coverage: 5.7% of statements
?       github.com/mongodb/terraform-provider-mongodbatlas/version      [no test files]

Datasource(s)

 make testacc TESTARGS='-run=TestAccDataSourceMongoDBAtlasEventTrigger'              [9:16:26]
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test $(go list ./... | grep -v /integration-testing) -v -parallel 20 -run=TestAccDataSourceMongoDBAtlasEventTrigger -timeout 300m -cover -ldflags="-s -w -X 'github.com/mongodb/terraform-provider-mongodbatlas/version.ProviderVersion=acc'"
?       github.com/mongodb/terraform-provider-mongodbatlas      [no test files]
=== RUN   TestAccDataSourceMongoDBAtlasEventTrigger_basic
--- PASS: TestAccDataSourceMongoDBAtlasEventTrigger_basic (32.42s)
=== RUN   TestAccDataSourceMongoDBAtlasEventTriggers_basic
=== PAUSE TestAccDataSourceMongoDBAtlasEventTriggers_basic
=== CONT  TestAccDataSourceMongoDBAtlasEventTriggers_basic
--- PASS: TestAccDataSourceMongoDBAtlasEventTriggers_basic (26.76s)
PASS
coverage: 5.6% of statements
ok      github.com/mongodb/terraform-provider-mongodbatlas/mongodbatlas 59.542s coverage: 5.6% of statements
?       github.com/mongodb/terraform-provider-mongodbatlas/version      [no test files]

Link to any related issue(s):
#512

Type of change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Documentation fix/enhancement

Required Checklist:

• I have signed the MongoDB CLA
• I have read the Terraform contribution guidelines
• I have added tests that prove my fix is effective or that my feature works per HashiCorp requirements
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code

Further comments

[themantissa]

LGTM! still needs APIx and DOU review

[andreaangiolillo]

LGTM

[thetonymaster]

LGTM