PR for 0.3.9 release

[wnojopra]

This release includes:

• dsub
  • Update version of cloudsdk docker image. Revert workaround for gsutil/gcloud bug, which should now be fixed in the updated image.
  • Update google-auth to 1.18.0 and pin google-api-core to 1.21.0
  • Remove all characters that are not a letter, number, or underscore when creating a name for command.
  • Move google_v2 arguments to google_common in the --help text.
  • Add a section for Google provider-specific command-line flags.
• Testing updates:
  • Re-enable the test e2e_errors.sh for all providers.
  • Add unit test for retrying BrokenPipeError
  • Fix ResourceWarning when running python unit tests.