Use BufferedOutputStream
Use BufferedOutputStream

Using BufferedOutputStream significantly speeds up the JAR creation. See testing section for an example.

Testing Done:
Green CI: https://travis-ci.org/pantsbuild/pants/builds/64236409

I used this command for benchmarking (+ flushing caches):
```
sudo /usr/sbin/purge && ls -alR > /dev/null && ./pants binary --no-use-nailgun macaw-swift/web-app::
```
Without BOS, the jar-tool step took 105, 112, and 123 seconds.
With BOS, the jar-tool step took 77, 80, and 85 seconds.

Bugs closed: 1596

Reviewed at https://rbcommons.com/s/twitter/r/2270/

laurentgo/pants,sameerparekh/pants,tdyas/pants,sid-kap/pants,jessrosenfield/pants,pombredanne/pants,pgroudas/pants,fkorotkov/pants,wisechengyi/pants,jtrobec/pants,cevaris/pants,landism/pants,peiyuwang/pants,twitter/pants,baroquebobcat/pants,pantsbuild/pants,scode/pants,megaserg/pants,lahosken/pants,ericzundel/pants,kslundberg/pants,di0spyr0s/pants,manasapte/pants,dturner-tw/pants,ity/pants,wisechengyi/pants,areitz/pants,tdyas/pants,pantsbuild/pants,scode/pants,UnrememberMe/pants,tdyas/pants,TansyArron/pants,peiyuwang/pants,megaserg/pants,peiyuwang/pants,digwanderlust/pants,jessrosenfield/pants,mateor/pants,TansyArron/pants,pgroudas/pants,lahosken/pants,wisechengyi/pants,benjyw/pants,benjyw/pants,twitter/pants,ericzundel/pants,jsirois/pants,scode/pants,pantsbuild/pants,peiyuwang/pants,kwlzn/pants,fkorotkov/pants,baroquebobcat/pants,mateor/pants,landism/pants,lahosken/pants,Gabriel439/pants,dbentley/pants,digwanderlust/pants,lahosken/pants,15Dkatz/pants,dturner-tw/pants,fkorotkov/pants,gmalmquist/pants,twitter/pants,jessrosenfield/pants,twitter/pants,tdyas/pants,pantsbuild/pants,dbentley/pants,wisechengyi/pants,tdyas/pants,sid-kap/pants,kwlzn/pants,landism/pants,ity/pants,gmalmquist/pants,15Dkatz/pants,areitz/pants,gmalmquist/pants,areitz/pants,dturner-tw/pants,TansyArron/pants,slyphon/pants,foursquare/pants,pgroudas/pants,15Dkatz/pants,pgroudas/pants,Gabriel439/pants,areitz/pants,twitter/pants,jessrosenfield/pants,kslundberg/pants,ericzundel/pants,scode/pants,manasapte/pants,peiyuwang/pants,benjyw/pants,pombredanne/pants,laurentgo/pants,twitter/pants,baroquebobcat/pants,megaserg/pants,manasapte/pants,cevaris/pants,TansyArron/pants,TansyArron/pants,wisechengyi/pants,scode/pants,sid-kap/pants,manasapte/pants,foursquare/pants,gmalmquist/pants,TansyArron/pants,pantsbuild/pants,sid-kap/pants,di0spyr0s/pants,jessrosenfield/pants,fkorotkov/pants,digwanderlust/pants,sameerparekh/pants,tdyas/pants,qma/pants,mateor/pants,di0spyr0s/pants,kwlzn/pants,pombredanne/pants,ity/pants,UnrememberMe/pants,sameerparekh/pants,laurentgo/pants,megaserg/pants,areitz/pants,fkorotkov/pants,dturner-tw/pants,qma/pants,ericzundel/pants,dturner-tw/pants,di0spyr0s/pants,twitter/pants,areitz/pants,sid-kap/pants,digwanderlust/pants,foursquare/pants,pombredanne/pants,laurentgo/pants,slyphon/pants,pgroudas/pants,jtrobec/pants,Gabriel439/pants,UnrememberMe/pants,jessrosenfield/pants,di0spyr0s/pants,ity/pants,manasapte/pants,tdyas/pants,ity/pants,UnrememberMe/pants,ity/pants,baroquebobcat/pants,jtrobec/pants,landism/pants,qma/pants,kslundberg/pants,twitter/pants,baroquebobcat/pants,benjyw/pants,cevaris/pants,15Dkatz/pants,digwanderlust/pants,wisechengyi/pants,megaserg/pants,foursquare/pants,Gabriel439/pants,pombredanne/pants,qma/pants,wisechengyi/pants,cevaris/pants,peiyuwang/pants,foursquare/pants,peiyuwang/pants,lahosken/pants,scode/pants,kslundberg/pants,digwanderlust/pants,qma/pants,sameerparekh/pants,jtrobec/pants,mateor/pants,baroquebobcat/pants,slyphon/pants,UnrememberMe/pants,pgroudas/pants,jtrobec/pants,dbentley/pants,Gabriel439/pants,manasapte/pants,twitter/pants,jsirois/pants,pombredanne/pants,manasapte/pants,mateor/pants,15Dkatz/pants,lahosken/pants,jtrobec/pants,tdyas/pants,landism/pants,baroquebobcat/pants,ity/pants,lahosken/pants,kwlzn/pants,15Dkatz/pants,fkorotkov/pants,sameerparekh/pants,kslundberg/pants,kslundberg/pants,Gabriel439/pants,15Dkatz/pants,foursquare/pants,pantsbuild/pants,dturner-tw/pants,15Dkatz/pants,wisechengyi/pants,scode/pants,laurentgo/pants,jtrobec/pants,benjyw/pants,megaserg/pants,di0spyr0s/pants,pombredanne/pants,UnrememberMe/pants,cevaris/pants,tdyas/pants,areitz/pants,foursquare/pants,mateor/pants,cevaris/pants,ericzundel/pants,baroquebobcat/pants,qma/pants,gmalmquist/pants,kwlzn/pants,UnrememberMe/pants,TansyArron/pants,baroquebobcat/pants,foursquare/pants,landism/pants,gmalmquist/pants,kslundberg/pants,jessrosenfield/pants,landism/pants,lahosken/pants,slyphon/pants,fkorotkov/pants,UnrememberMe/pants,slyphon/pants,mateor/pants,kwlzn/pants,dturner-tw/pants,sameerparekh/pants,ericzundel/pants,benjyw/pants,pantsbuild/pants,slyphon/pants,sid-kap/pants,dbentley/pants,peiyuwang/pants,sameerparekh/pants,foursquare/pants,wisechengyi/pants,qma/pants,landism/pants,mateor/pants,ericzundel/pants,megaserg/pants,slyphon/pants,kwlzn/pants,cevaris/pants,benjyw/pants,gmalmquist/pants,dbentley/pants,sid-kap/pants,fkorotkov/pants,dbentley/pants,di0spyr0s/pants,laurentgo/pants,ericzundel/pants,Gabriel439/pants,jsirois/pants,dbentley/pants,UnrememberMe/pants