Restore modified version of the #1314991 workaround for #1638563
    
    We're not seeing *exactly* #1314991 any more, but we're seeing
    something that looks quite similar: the first attempt to find
    updates just doesn't find any. No error message, no updates. I
    have reported a bug for this and am investigating it, in the
    meantime, let's restore the workaround, elaborated a bit, and
    looking for the 'Software is up to date' screen instead of the
    error message.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>