Draft: Zero friction to run autopkgtest

The merge request implements the following use case:

I just build a package, and want to test it with autopkgtest in a clean environment. When I run autopkgtest with no arguments, it auto-detects the binary packages I just got, the virtualization that the source package needs and the one my system can provide, and runs the tests for me.

There a few rough edges yet, but any feedback is appreciated.