Remove GenericBaseModel.get_cfn_attribute and improve stack failure reporting

[dominikschubert]

Changes

• Remove GenericBaseModel.get_cfn_attribute and unify code paths between legacy and new providers
• Improve stack failure reporting a tiny bit

Previously the ResourceStatusReason on the stack failure was empty, now it's set to the string representation of the caught exception. This is currently only enabled when CFN_VERBOSE_ERRORS is set though. We should probably make this the default though in the next minor release to increase parity.

New stack status:

{"LogicalResourceId": "stack-9645eb0a", "ResourceType": "AWS::CloudFormation::Stack", "ResourceStatus": "CREATE_FAILED", "ResourceStatusReason": "Resource type AWS::SSM::Parameter does not support attribute {Invalid}"}

We might also want to by start failing stacks by default when outputs can't be resolved but since this differs quite a bit from the current behavior I think we should have a deprecation path for this.

[github-actions]

LocalStack Community integration with Pro

       2 files         2 suites   1h 22m 51s ⏱️
2 297 tests 1 923 ✔️ 374 💤 0 ❌
2 298 runs  1 923 ✔️ 375 💤 0 ❌

Results for commit b621933.

♻️ This comment has been updated with latest results.

[coveralls]

coverage: 82.689% (+0.009%) from 82.68% when pulling b621933 on remove-get_cfn_attribute into 7710a0a on master.

[pinzon]

Awesome 🚀