https://bugzilla.redhat.com/show_bug.cgi?id=738725 documents that
'yum install libvirt' in Fedora 16 is rather noisy.  This fixes
the problems.

* libvirt.spec.in (%post client): Silence chkconfig warning about
SysV services.
(%post) [with_cgconfig]: Drop for Fedora 15 and newer, where
systemd does this automatically.