Baseline: de3c14da

Cherry picks:

   + a6bfab09:
     Automated rollback of commit
     64ac2a81.

Important changes:

  - Tests that fail to create or complete their
    `TestAttemptContinuation` by
    throwing an `ExecException` will report an `INCOMPLETE` status.
    Previously, Bazel
    would fail to report any status for the test attempt.

This release contains contributions from many people at Google, as well as divanorama, Fabian Meumertzheim, Keith Smiley, Marek uppa, Niyas Sait, Thi Doan, Yesudeep Mangalapilly.