Implement gnt-instance grow-disk

This patch exposes at command line level the grow-disk operation.

Reviewed-by: imsnah

scripts/gnt-instance

@@ -382,6 +382,21 @@ def DeactivateDisks(opts, args):
   return 0
 
 
+def GrowDisk(opts, args):
+  """Command-line interface for _ShutdownInstanceBlockDevices.
+
+  This function takes the instance name, looks for its primary node
+  and the tries to shutdown its block devices on that node.
+
+  """
+  instance = args[0]
+  disk = args[1]
+  amount = utils.ParseUnit(args[2])
+  op = opcodes.OpGrowDisk(instance_name=instance, disk=disk, amount=amount)
+  SubmitOpCode(op)
+  return 0
+
+
 def StartupInstance(opts, args):
   """Startup an instance.
 
@@ -1006,6 +1021,8 @@ commands = {
   'deactivate-disks': (DeactivateDisks, ARGS_ONE, [DEBUG_OPT],
                        "<instance>",
                        "Deactivate an instance's disks"),
+  'grow-disk': (GrowDisk, ARGS_FIXED(3), [DEBUG_OPT],
+                "<instance> <disk> <size>", "Grow an instance's disk"),
   'list-tags': (ListTags, ARGS_ONE, [DEBUG_OPT],
                 "<node_name>", "List the tags of the given instance"),
   'add-tags': (AddTags, ARGS_ATLEAST(1), [DEBUG_OPT, TAG_SRC_OPT],