Catch Bazaar/Breezy import errors and show them.
Review Request #13229 — Created Aug. 23, 2023 and submitted
brzfail to start due to an import error (such as a missing
Paramiko or another dependency), the error would be masked behind a
"Repository not found" error.
We now detect this and represent the error as an
SCMError, helping to
debug this both in production and during test runs.
Used this to debug some unit test failures. Verified that the exception
was represented properly.