Add run_train_net_forward_only() to LayersTestCase
Add run_train_net_forward_only() to LayersTestCase

Summary: Make it convenient to test a model where we don't care about the backward pass, e.g., when the backward pass won't be run anyway.

Reviewed By: xianjiec

Differential Revision: D4906890

fbshipit-source-id: 9da51a9de4422474ce780e180b1ca95d6bc8c46d

Yangqing/caffe2,bwasti/caffe2,bwasti/caffe2,davinwang/caffe2,sf-wind/caffe2,davinwang/caffe2,sf-wind/caffe2,bwasti/caffe2,sf-wind/caffe2,xzturn/caffe2,pietern/caffe2,davinwang/caffe2,pietern/caffe2,xzturn/caffe2,sf-wind/caffe2,bwasti/caffe2,bwasti/caffe2,Yangqing/caffe2,Yangqing/caffe2,davinwang/caffe2,Yangqing/caffe2,xzturn/caffe2,davinwang/caffe2,xzturn/caffe2,Yangqing/caffe2,pietern/caffe2,pietern/caffe2,caffe2/caffe2,pietern/caffe2,xzturn/caffe2,sf-wind/caffe2