app: monitor-config - do it all or nothing
    
    Don't keep trying to use a monitor config when it already failed for one
    monitor, otherwise virt-viewer can end up in a situation where none of
    the displays are enabled but the program is still running.
    So, in case of any failure, let's skip the whole monitor config, forcing
    virt-viewer to use the "fallback" one instead.
    
    Resolves: rhbz#1315206
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    Acked-by: Pavel Grunt <pgrunt@redhat.com>