Most of this deals with moving the libvirt-guests.sh script which
does all the work to /usr/libexec, so it can be shared by both
systemd and traditional init. Previously systemd depended on
the script being in /etc/init.d
Required to fix https://bugzilla.redhat.com/show_bug.cgi?id=789747
(cherry picked from commit d13155c20c)
