Don't install updates on support server if versions don't match
    
    I caught a few failed support_server update tests which failed
    because packages from the update weren't installed; they weren't
    installed because the update was for F28, but the support server
    runs on an F29 disk image. Obviously we should skip the 'install
    packages from the update' step in the support_server test unless
    the versions match.
    
    Arguably we could *never* install updates in support_server, but
    I think it's actually valuable to know if the update breaks
    support_server if we *are* on the right version.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>