Improve distributed training with LARS

[Yancey0623]

From latest meeting with Intel team:

https://arxiv.org/abs/1708.03888

[helinwang]

Should this be part of https://github.com/PaddlePaddle/Paddle/projects/30 or deferred for later? it seems an improvement rather than a core feature.

[Yancey0623]

Sure, it's just an improvement, and we can defer this improvement for later(after 201802).