SageMaker endpoint: enhance integ test coverage for failure conditions

[surajkota]

Description of changes:

• endpoint resource tests for both failure and recovery cases and asserts on conditions. See PR for details
• tests for retainAllVariantProperties used in udpateEndpoint code path
• enhance test coverage with multivariant endpoint config and using containers field instead or primary container and ImageConfig in model
• wrap up resource and reference creation to helper methods to reduce duplicate code. see k8s.load_and_create_resource and related methods
• bug fix: k8s.py helper methods related to conditions
  • wait_for_condition pre-maturely exited if the condition is nil. Depending on the case the condition maybe set later
  • _get_terminal_condition and is_resource_in_terminal_condition implementations was not correct, replaced with generic methods

Testing

Locally using pytest

Related PR: aws-controllers-k8s/sagemaker-controller#7

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[RedbackThomson]

These helper methods should make things a lot cleaner, and the fixtures much more clearly show the test setup as compared to our previous system. Thank you!

[jkuruba]

Not seeing where assert_condition_state_message is used

[surajkota]

test/e2e/sagemaker/tests/test_endpoint.py line#324

[jaypipes]

I presume a lot of the style-only changes are due to running black on the files, so this is fine. In the future, consider submitting separate PRs with style-only changes since that helps reviewers know what is a functional change and what isn't.