Fail fast for OSX CI runs.
Fail fast for OSX CI runs.

The Rube Goldberg machine that enables OSX CI for pants has a systemic
failure mode when using multiple shards.  The sha the shards need to
check out can be nuked by force pushes to the
https://github.com/pantsbuild/pants-for-travis-osx-ci repo in the
https://github.com/pantsbuild/pants CI job.  This change accounts for
this common and known failure mode by failing faster to try to up the
green throughput during periods of high commit volume on
https://github.com/pantsbuild/pants master.

Testing Done:
The new `.travis.osx.yml` linted green:
```console
jsirois@gill ~/dev/3rdparty/jsirois-pants4 (jsirois/osx-ci/fail-fast *) $ travis lint .travis.osx.yml
Hooray, .travis.osx.yml looks valid :)
```

CI went green here:
  https://travis-ci.org/pantsbuild/pants/builds/53747179

Bugs closed: 1232

Reviewed at https://rbcommons.com/s/twitter/r/1894/

qma/pants,wisechengyi/pants,pgroudas/pants,pgroudas/pants,lahosken/pants,baroquebobcat/pants,areitz/pants,ericzundel/pants,tdyas/pants,landism/pants,pombredanne/pants,dbentley/pants,dturner-tw/pants,di0spyr0s/pants,sameerparekh/pants,landism/pants,laurentgo/pants,peiyuwang/pants,peiyuwang/pants,landism/pants,wisechengyi/pants,UnrememberMe/pants,dbentley/pants,UnrememberMe/pants,qma/pants,15Dkatz/pants,baroquebobcat/pants,ericzundel/pants,di0spyr0s/pants,kslundberg/pants,foursquare/pants,peiyuwang/pants,slyphon/pants,areitz/pants,cevaris/pants,digwanderlust/pants,dturner-tw/pants,scode/pants,twitter/pants,qma/pants,ity/pants,megaserg/pants,jsirois/pants,kwlzn/pants,slyphon/pants,digwanderlust/pants,gmalmquist/pants,Gabriel439/pants,dgomez10/xanon,cevaris/pants,peiyuwang/pants,manasapte/pants,di0spyr0s/pants,tdyas/pants,foursquare/pants,15Dkatz/pants,Gabriel439/pants,dbentley/pants,ericzundel/pants,landism/pants,lahosken/pants,Gabriel439/pants,slyphon/pants,ericzundel/pants,ity/pants,dgomez10/xanon,lahosken/pants,kwlzn/pants,mateor/pants,15Dkatz/pants,laurentgo/pants,manasapte/pants,di0spyr0s/pants,jessrosenfield/pants,pgroudas/pants,benjyw/pants,areitz/pants,ity/pants,dbentley/pants,twitter/pants,gmalmquist/pants,dturner-tw/pants,sid-kap/pants,jessrosenfield/pants,digwanderlust/pants,TansyArron/pants,dgomez10/xanon,manasapte/pants,fkorotkov/pants,peiyuwang/pants,peiyuwang/pants,dturner-tw/pants,benjyw/pants,areitz/pants,TansyArron/pants,Gabriel439/pants,ericzundel/pants,foursquare/pants,foursquare/pants,15Dkatz/pants,qma/pants,dgomez10/xanon,slyphon/pants,benjyw/pants,kslundberg/pants,landism/pants,mateor/pants,scode/pants,benjyw/pants,lahosken/pants,pgroudas/pants,benjyw/pants,dgomez10/xanon,kslundberg/pants,Gabriel439/pants,TansyArron/pants,pombredanne/pants,15Dkatz/pants,mateor/pants,dturner-tw/pants,laurentgo/pants,tdyas/pants,di0spyr0s/pants,sameerparekh/pants,megaserg/pants,scode/pants,lahosken/pants,jtrobec/pants,wisechengyi/pants,laurentgo/pants,fkorotkov/pants,benjyw/pants,twitter/pants,megaserg/pants,TansyArron/pants,kwlzn/pants,kwlzn/pants,wisechengyi/pants,gmalmquist/pants,mateor/pants,areitz/pants,manasapte/pants,Gabriel439/pants,pantsbuild/pants,scode/pants,foursquare/pants,scode/pants,mateor/pants,lahosken/pants,pantsbuild/pants,jsirois/pants,jtrobec/pants,wisechengyi/pants,kslundberg/pants,cevaris/pants,wisechengyi/pants,digwanderlust/pants,slyphon/pants,manasapte/pants,UnrememberMe/pants,dbentley/pants,pombredanne/pants,megaserg/pants,foursquare/pants,landism/pants,di0spyr0s/pants,dturner-tw/pants,pombredanne/pants,jtrobec/pants,foursquare/pants,sameerparekh/pants,tdyas/pants,Gabriel439/pants,lahosken/pants,wisechengyi/pants,ity/pants,jtrobec/pants,landism/pants,jessrosenfield/pants,ericzundel/pants,tdyas/pants,qma/pants,baroquebobcat/pants,UnrememberMe/pants,ericzundel/pants,pantsbuild/pants,megaserg/pants,landism/pants,UnrememberMe/pants,sid-kap/pants,dgomez10/xanon,dgomez10/xanon,tdyas/pants,areitz/pants,cevaris/pants,fkorotkov/pants,digwanderlust/pants,mateor/pants,laurentgo/pants,UnrememberMe/pants,laurentgo/pants,baroquebobcat/pants,UnrememberMe/pants,gmalmquist/pants,kslundberg/pants,slyphon/pants,sameerparekh/pants,15Dkatz/pants,ity/pants,manasapte/pants,sid-kap/pants,twitter/pants,lahosken/pants,TansyArron/pants,wisechengyi/pants,fkorotkov/pants,tdyas/pants,15Dkatz/pants,megaserg/pants,benjyw/pants,manasapte/pants,qma/pants,cevaris/pants,wisechengyi/pants,foursquare/pants,jessrosenfield/pants,dgomez10/xanon,baroquebobcat/pants,di0spyr0s/pants,fkorotkov/pants,peiyuwang/pants,ericzundel/pants,sid-kap/pants,scode/pants,kwlzn/pants,pantsbuild/pants,jtrobec/pants,sid-kap/pants,twitter/pants,twitter/pants,sid-kap/pants,gmalmquist/pants,ity/pants,sameerparekh/pants,gmalmquist/pants,dbentley/pants,jsirois/pants,areitz/pants,peiyuwang/pants,twitter/pants,gmalmquist/pants,twitter/pants,tdyas/pants,foursquare/pants,jessrosenfield/pants,slyphon/pants,pgroudas/pants,sameerparekh/pants,pgroudas/pants,twitter/pants,cevaris/pants,pombredanne/pants,baroquebobcat/pants,baroquebobcat/pants,sameerparekh/pants,fkorotkov/pants,UnrememberMe/pants,dgomez10/xanon,pantsbuild/pants,dbentley/pants,digwanderlust/pants,pombredanne/pants,jessrosenfield/pants,kslundberg/pants,kwlzn/pants,jtrobec/pants,dgomez10/xanon,jessrosenfield/pants,kwlzn/pants,dturner-tw/pants,megaserg/pants,baroquebobcat/pants,TansyArron/pants,kslundberg/pants,baroquebobcat/pants,sid-kap/pants,pombredanne/pants,jtrobec/pants,TansyArron/pants,UnrememberMe/pants,tdyas/pants,qma/pants,15Dkatz/pants,pantsbuild/pants,mateor/pants,ity/pants,pantsbuild/pants,fkorotkov/pants,mateor/pants,scode/pants,dgomez10/xanon,fkorotkov/pants,cevaris/pants