The DBus conditional was renamed way back:

  commit da77f04e
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Thu Sep 20 15:05:39 2012 +0100

    Convert HAVE_DBUS to WITH_DBUS

but the shutdown inhibit code was not updated. Thus libvirt
was never inhibiting shutdown by a logged in user when VMs
are running.
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>