Add the -s option in the output of 'gnt-node'

Since on dual-homed clusters one always needs to add '-s' to the
gnt-node add command, make this appear in the output of 'gnt-node' (when
run without arguments).

Reviewed-by: imsnah

scripts/gnt-node

@@ -280,7 +280,7 @@ commands = {
            make_option("-s", "--secondary-ip", dest="secondary_ip",
                        help="Specify the secondary ip for the node",
                        metavar="ADDRESS", default=None),],
-          "<node_name>", "Add a node to the cluster"),
+          "[-s] <node_name>", "Add a node to the cluster"),
   'evacuate': (EvacuateNode, ARGS_FIXED(2),
                [DEBUG_OPT, FORCE_OPT],
                "[-f] <src_node> <dst_node>",