util: Initialize hooks at daemon shutdown if no hooks defined

We support to initialize the hooks at daemon reload if there is no
hooks script is defined, we should also support initialize the hooks
at daemon shutdown if no hooks is defined.

To address bz: https://bugzilla.redhat.com/show_bug.cgi?id=688859

src/util/hooks.c

@@ -209,7 +209,8 @@ virHookCall(int driver, const char *id, int op, int sub_op, const char *extra,
      */
     if ((virHooksFound == -1) ||
         ((driver == VIR_HOOK_DRIVER_DAEMON) &&
-         (op == VIR_HOOK_DAEMON_OP_RELOAD)))
+         (op == VIR_HOOK_DAEMON_OP_RELOAD ||
+         op == VIR_HOOK_DAEMON_OP_SHUTDOWN)))
         virHookInitialize();
 
     if ((virHooksFound & (1 << driver)) == 0)