Add warning on gnt-node add operation.

People might not have read all the documentation and might not expect their ssh configuration
and specially keys to be changed. Adding this warning will inform them before it happens.

Reviewed-by: iustinp

scripts/gnt-node

@@ -30,6 +30,10 @@ from ganeti import utils
 
 def AddNode(opts, args):
   """Add node cli-to-processor bridge."""
+  logger.ToStderr("-- WARNING -- \n"
+    "Performing this operation is going to replace the ssh daemon keypair\n"
+    "on the target machine (%s) with the ones of the current one\n"
+    "and grant full intra-cluster ssh root access to/from it\n" % args[0])
   op = opcodes.OpAddNode(node_name=args[0], secondary_ip=opts.secondary_ip)
   SubmitOpCode(op)