Proposal: Kubernetes Build Plugin

We propose that a build plugin and corresponding framework be added to kubernetes to facilitate: 

1. Leveraging Kubernetes' scheduling, resource allocation, and garbage collection in order to provide docker image build capabilities to users
2. Third party systems wishing to use OTS Kubernetes as a build-farm
3. Organizations using a third-party CI server to orchestrate docker image builds as part of their devops SOPs
As dicussed in https://github.com/GoogleCloudPlatform/kubernetes/issues/391 it does require that K8s support priviledged mode containers.