* mandos: Never call .Reset() on a defunct Avahi entry group.
(AvahiService.remove): Only do group.Reset(), as before.
(AvahiService.add): Only create new group if necessary.
(AvahiService.cleanup): Also do group.Free() if a group exists.
(AvahiService.server_state_changed): Call .cleanup() on errors.
Also log error parameter, if
passed.