[libvirt] [RFC] daemon: remove hardcode dep on libvirt-guests

Hi, all. In virtuozzo mgmt we do not use libvirt-guests service. First because we need do extra steps on domain start and second we want to decice whether to suspend or to shutdown a domain on per domain basis. Starting is not the problem but system shutdown is. As domain in systemd based systems is just another unit we need to set ordering dependency so that domain will not be killed before mgmt service as ba79e387 do for libvirt-guest service. So let's remove this hardcode. I see 2 options. 1. Take dependant service name from config. 2. Introduce intermediate service that will specify real dependency. Looks like this one is more flexible. By the way AFAIK this is the only place that harcode libvirt-guests in libvirtd. Nikolay