Fork from sYnfo/dbs
improve builder:

use standard celery api, not send_task
target_registry -> target_registries
hook submit_results to build_image
Fix a typo
Document GitPython as dependency
task_api is part of server, not worker
Revert "task_api is part of server, not worker"

This reverts commit 179523abf12983b958bec46449f9ad511a303549.
new task: building inside privileged docker container
move README.md to README-worker.md
Merge branch 'master' of DBuildService/dbs-worker
move stuff to right places, fix imports, fix task invocation, spec, ...