bluebox: support a language group
bluebox: support a language group

This allows for .travis.ymls with "group: dev", for example.

solarce/worker,henrikhodne-abandoned/worker,Acidburn0zzz/worker,henrikhodne-abandoned/worker,solarce/worker,travis-ci/worker,Acidburn0zzz/worker,travis-ci/worker,solarce/worker,travis-ci/worker,Acidburn0zzz/worker,henrikhodne-abandoned/worker