fp16: add test for FC
fp16: add test for FC

Summary:
fp16 and TensorCore support was already added to the op in https://github.com/caffe2/caffe2/pull/1056. This adds a test.
Closes https://github.com/caffe2/caffe2/pull/1182

Differential Revision: D5794698

Pulled By: akyrola

fbshipit-source-id: b0d7ef317dfbb9d712b0b4646b38dc600b8434f1

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