Debian support is not maintained in Kolla so it got a bit behind Ubuntu
one. This changeset enables Debian for all images. Jessie (even with
backports) may be too old for some images though.
Also unify distro check to ['debian', 'ubuntu'] to keep alphabetical order
like it is done for RPM distributions.
Partially-Implements: blueprint multiarch-and-arm64-containers
Change-Id: I056233fbfa277e0e2360c07c3f80d9558c554357