Add each GCE instance to an instance group
Add each GCE instance to an instance group

if an instance group name is provided

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