Add a full suite of presets for libvirt services for Debian/Ubuntu
    
    Most, if not all, service units require configuration before enabling.
    Unfortunately, Debian/Ubuntu tend to enable and start services by
    default even when it makes absolutely no sense to do so. And by doing
    so, this can cause abnormal failures when it's unwanted.
    
    To prevent crashes and abnormal failures, set up the preset to disable
    all units except libvirtd.service by default.