Debian support

[kpcyrd]

This is the tracking issue for Debian support. The list of current issues:

• Collect packages currently in debian: The rebuilderd scheduler expects a list of all packages that it needs to issue rebuilds for
• Map packages to buildinfo files: Debian has detached buildinfo files so there's some code needed to locate the right buildinfo file before we can attempt to rebuild a package
• Integrate debrebuild.py with rebuilderd
• binNMUs: binary non-maintainer uploads are used to build the package again in a more recent build environment. The buildinfo file uses the "binNMU version" but the files published to the apt repository only contains the version of the initial source upload, which means we're unable locate the correct buildinfo file.