Tweak how update-upgrade tests are handled a bit
    
    Looking at this, it's a bit weird: the updated packages are
    actually included in the upgrade process, but we still run
    _advisory_update, which does basically nothing...then reboots.
    That's kinda silly and makes the tests a bit flaky, let's fix
    it. I don't think there's actually any problem with doing the
    upload of updatepkgs.txt in _repo_setup_updates, becase that
    already guards against being run more than once, it just bails
    very early if it's already been run.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>