Test failures aren't properly reported in Gubernator

[jlewi]

If steps in our Airflow E2E test pipeline fail, we should create junit files in GCS so that gubernator shows the test as failed.

Similarly, we should probably create junit files corresponding to any steps that don't run because of upstream failures.

Otherwise in Gubernator if a step fails we just see 0 failed/ N succeeded where N is less than the total number of tests. This is confusing for people looking at the tests.

One way to fix this would be to have the final step in our Airflow pipeline create any missing junit files in gubernator.

context:
#222 (comment)

[jlewi]

This has been fixed.

[jlewi]

This was addressed by #319