Revert changes in blob name in optimizer
Revert changes in blob name in optimizer

Summary: A while ago, we had to change some blob names in `optimizer.py` (more specifically, names of `iteration_mutex` and `optimizer_iteration`) to handle corner cases when preparing a net for parallel execution.

Reviewed By: azzolini

Differential Revision: D6480819

fbshipit-source-id: a03a7aa9fad322a50e7785914b0eb0f8654e6d90

Yangqing/caffe2,xzturn/caffe2,xzturn/caffe2,xzturn/caffe2,Yangqing/caffe2,xzturn/caffe2,Yangqing/caffe2,caffe2/caffe2,Yangqing/caffe2,xzturn/caffe2,Yangqing/caffe2