hooks: Fix a wrong description

In the definition of virHookQemuOpType and virHookNetworkOpType,
we should use 'stopped' rather than 'shutdown'.
Signed-off-by: NChen Hanxiao <chenhanxiao@gmail.com>

docs/hooks.html.in

@@ -316,7 +316,7 @@
           executes <b>prior</b> to the object (guest or network) being created.
           This allows the object start operation to be aborted if the script
           returns indicating failure.<br/><br/></li>
-      <li>The "shutdown" operation for the guest and network hook scripts,
+      <li>The "stopped" operation for the guest and network hook scripts,
           executes <b>after</b> the object (guest or network) has stopped. If
           the hook script indicates failure in its return, the shut down of the
           object cannot be aborted because it has already been performed.