This is a reland of commit 05381726

The change was not related to the errors that it was reverted for, so no
changes are necessary.

Original change's description:
> Set a default got_revision property in the bot_update json output.
>
> The bot_update.py script sets a got_revision property by default even if
> it is not present in the reverse revision mapping. This results in an
> uncaught exception when set_output_commit is set to True if got_revision
> isn't present in the reverse revision mapping, but it isn't caught until
> production because the test API doesn't match that behavior. This change
> updates the test API method to match the behavior of the script.
>
> Recipe-Nontrivial-Roll: build
> Recipe-Nontrivial-Roll: build_limited
> Recipe-Nontrivial-Roll: chromiumos
> Recipe-Nontrivial-Roll: infra
> Change-Id: Ideefa9d77d2a816ae66a2bb52737264ed3f5bcee
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3575361
> Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
> Reviewed-by: Josip Sokcevic <sokcevic@google.com>
> Commit-Queue: Garrett Beaty <gbeaty@google.com>
> Auto-Submit: Garrett Beaty <gbeaty@google.com>

Recipe-Nontrivial-Roll: build
Recipe-Nontrivial-Roll: build_limited
Recipe-Nontrivial-Roll: chromiumos
Recipe-Nontrivial-Roll: infra
Change-Id: I80efeee8a2b951df43b00d89bb596dc2cf2fcec7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3582182Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@google.com>