<check-sources> Bug 1024532 - add and refine "fail-then-bail" workflow
https://bugzilla.redhat.com/show_bug.cgi?id=1024532

This addresses the missing repo error from the bug report and adds
logic to stop after a class of issue (missing repo, disabled repo,
etc.) has been detected.

Also:

* set the exit code to `0` if no problems are detected, `1` otherwise

* improve subscription type and version detection

* moved yum-plugin-priorities check to be right before the dependent checks

* repaired ose-2.0 repoids in `repo_db` - they seem to have changed at
  some point in the past week?

Work remains - the fail-then-bail workflow applies to the `--fix`
option as well, which might not be what we want