Allow post-release pocket uploads in private PPAs

[Julian Edwards]

To support security uploads to the security team's private PPA, we need to allow uploads to post-release pockets. (-security in this case).

This is because the archive admins / distro team want to see the upload going to -security in the changelog.

[Julian Edwards (julian-edwards)]

This is not needed, the PPA upload path can be used to override the pocket, so the security team can upload to ~<ppaname>/<distro>/<suite> and keep their old changes files and changelog that contain -security.