Support privileged containers in a pod

Add a Privileged field to containers in a pod, in order to facilitate pods
performing administrative tasks such as builds via Docker-in-Docker.

Discussion: https://github.com/GoogleCloudPlatform/kubernetes/issues/391
Add temporary support for container-scoped run-once restart policy

To facilitate pods use cases beyond long-running services, introduce a simple
temporary container-scoped run-one pod restart policy.

Should be eventually superceded by the following upstream feature:

https://github.com/GoogleCloudPlatform/kubernetes/issues/127
Introduce BuildConfig type

Add BuildConfig, a new REST object which defines the template for a build.
Implement a simple build system

A simple build system implementation based upon the BuildConfig API. Introduces
a new Build REST object which represents the state of a build at a point in time.

The BuildController manages builds by examining the states of build-associated pods
and modeling build behavior using a state machine pattern.