High: stonith-ng's function cannot be blocked with CIB updates forever

In the high-load (or high-rate-config-change) scenarios,
pacemaker-fenced would be unable to provide service when basically DoS'd
with CIB update notifications.  Try to reconcile that with elevated
priority of the server's proper listening interface in the mainloop, at
worst, it will try to fence with slightly outdated config, but appears
to be less bad than not carrying the execution at all, for instance.
Other daemons might be considered as well.

Prerequisites:
- ClusterLabs/libqb#352

How to verify:
- mocked/based -N (see commit adding that module to mocked based daemon)

lib/common/utils.c

@@ -1031,7 +1031,8 @@ attrd_ipc_server_init(qb_ipcs_service_t **ipcs, struct qb_ipcs_service_handlers
 void
 stonith_ipc_server_init(qb_ipcs_service_t **ipcs, struct qb_ipcs_service_handlers *cb)
 {
-    *ipcs = mainloop_add_ipc_server("stonith-ng", QB_IPC_NATIVE, cb);
+    *ipcs = mainloop_add_ipc_server_with_prio("stonith-ng", QB_IPC_NATIVE, cb,
+                                              QB_LOOP_HIGH);
 
     if (*ipcs == NULL) {
         crm_err("Failed to create fencer: exiting and inhibiting respawn.");