Created by: jacquesqiao

In this design(https://github.com/PaddlePaddle/Paddle/blob/develop/doc/design/cluster_train/pserver_client.md) we don't have a update() interface for update parameter, I guess we want to do this immediately after call paddle_send_grads.

My question is, do we need to add a update function for updating parameter by pserver cclient？