backend/gce: add comments to all exported types and functions
backend/gce: add comments to all exported types and functions

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