[Test] Fix export-image-logs race by exporting while stack still exists

[gmarciani]

Description of changes

Fix export-image-logs race by exporting while stack still exists

In test_build_image, export logs as soon as the build log stream is available (while BUILD_IN_PROGRESS) so the build-image stack is guaranteed to exist, instead of after BUILD_COMPLETE when it self-deletes.

Also validate export from a failed build, whose stack and log stream are retained.
Notice that we already export image logs if the image fails in test_build_image to capture logs for troubleshooting. However we do not assert on that command to succeed. That's the reason why we added the assertion on test test_build_image_wrong_pcluster_version

Tests

SUCCESS (Same test [params that reported the failure)

test-suites:
  createami:
    test_createami.py::test_build_image:
      dimensions:
      - instances:
        - g4dn.2xlarge
        oss:
        - rhel8
        regions:
        - us-west-2
        schedulers:
        - slurm
    test_createami.py::test_build_image_wrong_pcluster_version:
      dimensions:
      - instances:
        - g4dn.2xlarge
        oss:
        - rhel8
        regions:
        - us-west-2

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

[github-actions]

✅ Cherry-pick to develop opened: #7486