Set the service provider to systemd for Fedora >= 18

init no longer works as the service provider for libvirtd on F18
https://bugzilla.redhat.com/show_bug.cgi?id=903871

Change-Id: I1423f7c761a351a4a33913c8698028df4f447092
Merge "Set the service provider to systemd for Fedora >= 18"