Currently we weren't testing the deb backaned for sstate correctness
and there was a bug that had crept in. Ensure we cover all package
backends with the test regardless of what the distro/conf sets.
(From OE-Core rev: cdaafc3729700778d95afc2413553d7b41c1317b)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>