fix distribution detection in apt_repository module, so it also work
on Mint as it work on Debian, fix #4587.

PPAs are not supported however, since that's a Ubuntu specific feature
and mint is detected as a generic distribution and use a different
codename than the Ubuntu release it is based on, which mean that apt_repository
cannot add detect and add the proper url without a better heuristic.
Merge pull request #4594 from mscherer/fix_4587

fix distribution detection in apt_repository module, so it also work on mint as it work on Debian, partially fix #4587