Re-wrap a paragraph to eliminate a sphinx warning

This just makes sure that the paragraph doesn't contains lines that
start with :, which make Sphinx (1.0.7) complain.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

doc/admin.rst

@@ -291,8 +291,8 @@ While the command to stop one is::
 
 .. warning:: Do not use the Xen or KVM commands directly to stop
    instances. If you run for example ``xm shutdown`` or ``xm destroy``
-   on an instance Ganeti will automatically restart it (via the
-   :command:`ganeti-watcher` command which is launched via cron).
+   on an instance Ganeti will automatically restart it (via
+   the :command:`ganeti-watcher` command which is launched via cron).
 
 Querying instances
 ~~~~~~~~~~~~~~~~~~