bugfix htrace_to_chrome wrong output file name
bugfix htrace_to_chrome wrong output file name

Summary:
This is a quick bugfix on `htrace_to_chrome.py`, which produces outputs with wrong file names if command line arguments are given in a specific way.

  fbcode $ python caffe2/caffe2/contrib/prof/htrace_to_chrome.py --display operator /tmp/htrace_alexnet_span_log_20161224_055901
  Writing chrome json file to --display.json
  Now import --display.json in chrome://tracing

Differential Revision: D4369445

fbshipit-source-id: 628f4dbd88fb86814a0d92cd4c8407ba12a401d0

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