Add a dummy workunit to the end of the run to print out a timestamp that includes the time spent in the last task.
Add a dummy workunit to the end of the run to print out a timestamp that includes the time spent in the last task.

I noticed some runs seem to hang a long time between the printing of the last timestamp and exiting.

Add a dummy workunit to the end of the run to print out a timestamp that includes the time spent in the last task.

Testing Done:
After this change, I get a timestamp that accounts for the missing time:

```
09:27:19 00:00 [main]
               (To run a reporting server: ./pants server)
09:27:19 00:00   [bootstrap]
09:27:23 00:04   [setup]
09:27:23 00:04     [parse]
               Executing tasks in goals: bootstrap -> imports -> unpack-jars -> deferred-sources -> gen -> resolve -> compile
09:27:26 00:07   [bootstrap]
09:27:26 00:07     [bootstrap-jvm-tools]
09:27:26 00:07   [imports]
09:27:26 00:07     [ivy-imports]
09:27:30 00:11   [unpack-jars]
09:27:30 00:11     [unpack-jars]
09:27:30 00:11   [deferred-sources]
09:27:30 00:11     [deferred-sources]
09:27:30 00:11   [gen]
09:27:30 00:11     [thrift]
09:27:30 00:11     [protoc]
09:27:30 00:11     [antlr]
09:27:31 00:12     [ragel]
09:27:31 00:12     [jaxb]
09:27:31 00:12     [wire]
09:27:31 00:12     [aapt]
09:27:31 00:12   [resolve]
09:27:31 00:12     [ivy]
09:27:32 00:13       [ivy-resolve]
09:27:40 00:21   [compile]
09:27:40 00:21     [compile]
09:27:40 00:21     [jvm]
09:27:40 00:21       [jvm-compilers]
09:27:59 00:40   [complete]
               SUCCESS
```

CI is green at https://travis-ci.org/pantsbuild/pants/builds/57973122

Bugs closed: 1375, 1393

Reviewed at https://rbcommons.com/s/twitter/r/2054/

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