When failing during workflow.run, post a generic failure like we do during events

[marco-c]

When an exception is thrown during the bot workflow, we report a build failure without any additional information:

code-review/bot/code_review_bot/cli.py

Line 177 in 71390ca

w.update_status(revision, state=BuildState.Fail)

.

We should instead add at least a message like events does in case of generic failures:

code-review/events/code_review_events/workflow.py

Line 203 in 71390ca

failure = UnitResult(

.