Use new RPC call in “gnt-node list”

Reviewed-by: iustinp

scripts/gnt-node

@@ -78,8 +78,7 @@ def ListNodes(opts, args):
   else:
     selected_fields = opts.output.split(",")
 
-  op = opcodes.OpQueryNodes(output_fields=selected_fields, names=[])
-  output = SubmitOrSend(op, opts)
+  output = GetClient().QueryNodes([], selected_fields)
 
   if not opts.no_headers:
     headers = {