Add an elapsed timestamp to the banner for CI.
Add an elapsed timestamp to the banner for CI.

Looks like:

```
[== 00:00 Banner message ==]
```

Testing Done:
See: https://travis-ci.org/pantsbuild/pants/jobs/50841075 for example output

Bugs closed: 1109

Reviewed at https://rbcommons.com/s/twitter/r/1775/

sameerparekh/pants,15Dkatz/pants,kslundberg/pants,dgomez10/xanon,landism/pants,twitter/pants,pgroudas/pants,pantsbuild/pants,scode/pants,scode/pants,kwlzn/pants,kwlzn/pants,megaserg/pants,foursquare/pants,mateor/pants,slyphon/pants,kwlzn/pants,sid-kap/pants,benjyw/pants,UnrememberMe/pants,UnrememberMe/pants,ity/pants,mateor/pants,laurentgo/pants,wisechengyi/pants,jtrobec/pants,foursquare/pants,laurentgo/pants,digwanderlust/pants,digwanderlust/pants,qma/pants,twitter/pants,UnrememberMe/pants,manasapte/pants,cevaris/pants,ericzundel/pants,dbentley/pants,landism/pants,scode/pants,tdyas/pants,peiyuwang/pants,slyphon/pants,dturner-tw/pants,peiyuwang/pants,slyphon/pants,dgomez10/xanon,pantsbuild/pants,fkorotkov/pants,lahosken/pants,kwlzn/pants,Gabriel439/pants,pantsbuild/pants,fkorotkov/pants,jsirois/pants,digwanderlust/pants,UnrememberMe/pants,sameerparekh/pants,15Dkatz/pants,ity/pants,15Dkatz/pants,mateor/pants,baroquebobcat/pants,fkorotkov/pants,digwanderlust/pants,baroquebobcat/pants,sid-kap/pants,jessrosenfield/pants,tejal29/pants,pantsbuild/pants,foursquare/pants,laurentgo/pants,kslundberg/pants,ity/pants,peiyuwang/pants,dbentley/pants,twitter/pants,megaserg/pants,jessrosenfield/pants,twitter/pants,peiyuwang/pants,gmalmquist/pants,cevaris/pants,fkorotkov/pants,wisechengyi/pants,15Dkatz/pants,gmalmquist/pants,twitter/pants,tejal29/pants,lahosken/pants,cevaris/pants,peiyuwang/pants,kslundberg/pants,UnrememberMe/pants,ericzundel/pants,cevaris/pants,pombredanne/pants,manasapte/pants,slyphon/pants,Gabriel439/pants,benjyw/pants,di0spyr0s/pants,areitz/pants,tejal29/pants,UnrememberMe/pants,cevaris/pants,foursquare/pants,TansyArron/pants,kslundberg/pants,peiyuwang/pants,dbentley/pants,baroquebobcat/pants,mateor/pants,15Dkatz/pants,jsirois/pants,sameerparekh/pants,manasapte/pants,pantsbuild/pants,fkorotkov/pants,15Dkatz/pants,benjyw/pants,foursquare/pants,gmalmquist/pants,landism/pants,TansyArron/pants,UnrememberMe/pants,lahosken/pants,dbentley/pants,ity/pants,tejal29/pants,TansyArron/pants,slyphon/pants,tdyas/pants,sid-kap/pants,wisechengyi/pants,qma/pants,dgomez10/xanon,fkorotkov/pants,jtrobec/pants,digwanderlust/pants,mateor/pants,twitter/pants,tdyas/pants,twitter/pants,baroquebobcat/pants,jtrobec/pants,slyphon/pants,15Dkatz/pants,foursquare/pants,tdyas/pants,jessrosenfield/pants,dgomez10/xanon,dgomez10/xanon,kslundberg/pants,fkorotkov/pants,Gabriel439/pants,UnrememberMe/pants,ericzundel/pants,megaserg/pants,di0spyr0s/pants,pgroudas/pants,manasapte/pants,megaserg/pants,qma/pants,di0spyr0s/pants,Gabriel439/pants,twitter/pants,qma/pants,TansyArron/pants,scode/pants,manasapte/pants,megaserg/pants,gmalmquist/pants,pombredanne/pants,mateor/pants,dbentley/pants,fkorotkov/pants,foursquare/pants,ity/pants,pombredanne/pants,jtrobec/pants,baroquebobcat/pants,ericzundel/pants,kwlzn/pants,laurentgo/pants,dturner-tw/pants,sid-kap/pants,wisechengyi/pants,TansyArron/pants,cevaris/pants,pombredanne/pants,kslundberg/pants,slyphon/pants,ericzundel/pants,tdyas/pants,areitz/pants,landism/pants,sid-kap/pants,dgomez10/xanon,megaserg/pants,baroquebobcat/pants,wisechengyi/pants,di0spyr0s/pants,wisechengyi/pants,dturner-tw/pants,ericzundel/pants,ity/pants,dgomez10/xanon,dturner-tw/pants,benjyw/pants,gmalmquist/pants,digwanderlust/pants,dbentley/pants,landism/pants,foursquare/pants,jessrosenfield/pants,tdyas/pants,benjyw/pants,peiyuwang/pants,lahosken/pants,kwlzn/pants,dgomez10/xanon,qma/pants,lahosken/pants,sid-kap/pants,jtrobec/pants,di0spyr0s/pants,foursquare/pants,sameerparekh/pants,landism/pants,baroquebobcat/pants,mateor/pants,laurentgo/pants,pgroudas/pants,dturner-tw/pants,tdyas/pants,lahosken/pants,baroquebobcat/pants,manasapte/pants,ericzundel/pants,lahosken/pants,megaserg/pants,wisechengyi/pants,TansyArron/pants,dturner-tw/pants,tdyas/pants,manasapte/pants,ericzundel/pants,scode/pants,areitz/pants,peiyuwang/pants,jtrobec/pants,scode/pants,pgroudas/pants,sid-kap/pants,dbentley/pants,wisechengyi/pants,jessrosenfield/pants,ity/pants,baroquebobcat/pants,tejal29/pants,areitz/pants,jsirois/pants,sameerparekh/pants,landism/pants,kslundberg/pants,pgroudas/pants,pombredanne/pants,sameerparekh/pants,di0spyr0s/pants,pantsbuild/pants,wisechengyi/pants,twitter/pants,Gabriel439/pants,scode/pants,UnrememberMe/pants,Gabriel439/pants,qma/pants,kwlzn/pants,jessrosenfield/pants,Gabriel439/pants,dturner-tw/pants,dgomez10/xanon,mateor/pants,tdyas/pants,areitz/pants,jessrosenfield/pants,gmalmquist/pants,benjyw/pants,areitz/pants,laurentgo/pants,pgroudas/pants,di0spyr0s/pants,qma/pants,benjyw/pants,lahosken/pants,jtrobec/pants,pombredanne/pants,TansyArron/pants,pombredanne/pants,areitz/pants,landism/pants,dgomez10/xanon,sameerparekh/pants,dgomez10/xanon,gmalmquist/pants,15Dkatz/pants,pantsbuild/pants,cevaris/pants