Fedora 33 release housekeeping: update test data etc.
    
    Update allstable.json, the imagelists, the archive cutoff
    release, and adjust tests and so on for those changes. Also
    update the new _Appliance subvariants a bit as this is necessary
    for the tests to pass, and enhance the 'check expected images'
    code to handle that ARM images now may or may not have _Appliance
    suffixes on the subvariant value, likewise now needed for tests
    to pass since we have F33 data.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>