Fix ImageInput op in resnet50_trainer.py
Fix ImageInput op in resnet50_trainer.py

Summary:
Fix #1269 (from fa0fcd4053dd42a4ec3a2a12085662179f0e11df).
Closes https://github.com/caffe2/caffe2/pull/1314

Reviewed By: bwasti

Differential Revision: D6021171

Pulled By: bddppq

fbshipit-source-id: 7d7c45f8b997c25f34530f826729d700a9c522d4

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