add speed benchmark tool
add speed benchmark tool

Summary: provide a easy way to benchmark different dper models.

Differential Revision: D4367258

fbshipit-source-id: 4821645c58ad183becf0c82daae991375d5c6ef4

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