[report-hook] take location of bugs.txt from the command line
[report-hook] take location of bugs.txt from the command line

Summary:
This was hardcoded but it's passed as an option to the script. It can be useful to generate text reports from arbitrary json reports, eg:

  ./infer/lib/python/report.py --issues-json infer-out/report.json --project-root . --results-dir infer-out --issues-txt foo.txt

Reviewed By: martinoluca

Differential Revision: D5526683

fbshipit-source-id: 3f9c3ee

blzq/infer,ropas/infer,jvillard/infer,jvillard/infer,jvillard/infer,blzq/infer,facebook/infer,ropas/infer,jvillard/infer,jvillard/infer,ropas/infer,ropas/infer,facebook/infer,blzq/infer,blzq/infer,ropas/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,facebook/infer,blzq/infer,ropas/infer,jvillard/infer,blzq/infer,jvillard/infer