This patch fixes the URLs for the stretch-queens Debian repo.
First, it uses the now standardized scheme for the backport
URL: http://<debian-release>-<openstack-release>.debian.net/debian,
maintained by the Debian OpenStack team.
Then it uses $::lsbdistcodename everywhere, to be able to work
with all Debian releases.
Finally, this patch fixes unit tests to work with stretch and queens
as default.
Change-Id: I96af5021c51d6db9946197f8bc187a386ae04f25
Co-Authored-By: Alex Schultz <aschultz@redhat.com>