Build Kubernetes in Docker

Scripts and Dockerfile to build a container image, build binaries, run tests, etc.  Also copy output back out to the host machine.

The full flow isn't there yet, but this should work for building the basic binaries.  More to follow for building releases.
Yes -- but that ends up copying our .git directory and the output directory back up as context on every build.  Doing this takes things down from >60M to ~250k.