Serious regression of "systemctl restart libvirtd.service" in F17

[Laine Stump]

See

https://bugzilla.redhat.com/show_bug.cgi?id=805942

which describes the problem (all dnsmasq/qemu-kvm/etc processes started
by libvirtd are killed by libvirtd restart) and

https://www.redhat.com/archives/libvir-list/2012-March/msg00946.html

which has an earlier fix to part of the problem, and the discussion that
led to the above bug being filed.