Code review comment for lp:~pwlars/ubuntu-test-cases/bootest-no-revision

We need to keep the ability to override the default revision and override with something specific. This would be necessary if the latest image is unbootable and we roll back to the prior revision to keep proposed-migration testing moving. But setting this to '81' is also not the desired behavior, we should use '0' to default to the latest revision.

This revision override is one of the motivations for the boottestrc file. Perhaps there is a better way to achieve this overall goal.