update_sync: fix Bodhi queries when F33M release doesn't exist
    
    Not all releases exist all the time. Currently F33 and F33C releases exist, but
    F33M doesn't. With the existing code, that completely breaks all F33 update
    querying. So instead, retreive the list of releases known to Bodhi and only
    skip those which are not known, instead of all-or-nothing approach. F33 updates
    now correctly show up with this patch.
    
    Merges: https://pagure.io/fedora-qa/blockerbugs/pull-request/128