Replace Job() and JobStatus() with typesafe versions, and introduce JobType()
for the rare instances where we don't know the type up front.
Additionally, catch a few more error cases:
- if OSBuildResult is nil, then we failed to invoke osbuild
- make sure the same JobResult handling is done for osbuild-koji, as for osbuild
Since the workers will use structured error messages
going forward, it is necessary to maintain backwards
compatability for there errors in composer. Tests have
been added to the various apis to ensure that each api
checks for both kinds of errors, old and new.
