remote: make system libvirtd exit when idle via timeout

remote: make system libvirtd exit when idle via timeout

Since we have socket activation available now, we can let the system
libvirtd exit when it is idle. This allows it to still do autostart
when the host boots up, but when nothing was started it will quickly
exit again until some mgmt app connects to the socket.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>