Make bb gh merge more robust


Pull request for [Make bb gh merge more robust](https://trello.com/c/lqaQ4SO1/1927-make-bb-gh-merge-more-robust).

From Circle support:

```
Hi Almad,

I think the best way to tell if it's still running is to check the stop_time. If it's null, it's still running.

Thanks,
-Emile
```
    
`while not build.get('stop_time'):`