Code review comment for lp:~jelmer/launchpad/publisher-use-debian-1

I haven't done a pre-implementation call about this specific change, although I have discussed moving towards more use of python-debian (which is an upstream project maintained by various Debian and Ubuntu developers) with Julian in the past.

I'm about to make some more changes to this particular part of the code, and it seemed like a good idea to refactor first and use python-debian's infrastructure so that I don't have to worry about the serialization of newly introduced fields.

Tests: ./bin/test lp.archivepublisher

I've fixed all remaining lint issues.