spec: require dbus-daemon when using libvirtd in Fedora

https://bugzilla.redhat.com/show_bug.cgi?id=830201

In older Fedora, the spec file for libivrt depended on avahi, which
included avahi-daemon, which in turn depended on dbus.  But now that
avahi libs and avahi-daemon are (correctly) in separate pacakges,
and since we REALLY don't want a mandatory dependency on avahi-daemon,
and considering that our init scripts require the messagebus service
from dbus, we need to explicitly require dbus ourselves.

* libvirt.spec.in (Requires): Add dbus for libvirt-daemon.

libvirt.spec.in

@@ -712,6 +712,8 @@ Requires(postun): systemd-units
 %if %{with_numad}
 Requires: numad
 %endif
+# libvirtd depends on 'messagebus' service
+Requires: dbus
 
 %description daemon
 Server side daemon required to manage the virtualization capabilities