UNUSED_VARIABLE VS compile fail fix
UNUSED_VARIABLE VS compile fail fix

Summary:
fix test projects UNUSED_VARIABLE compile fail on visual studio
Closes https://github.com/caffe2/caffe2/pull/613

Differential Revision: D5121541

Pulled By: Yangqing

fbshipit-source-id: c353e8df4995e732e4d5d64bac15d849464efea2

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