Do not initialize BN params if init_params is false.
Do not initialize BN params if init_params is false.

Summary:
If init_params is False, the parameters should not be initialized.
This is particularly important when testing a model that provides values for these BN parameters.
Closes https://github.com/caffe2/caffe2/pull/174

Differential Revision: D4621791

Pulled By: Yangqing

fbshipit-source-id: 518443925990a12c1d5729b0971ebe19ba5d8998

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