We also add "version" to all docker images and containers
This version is to be incremented manually when we change the shape of the build
image (like changing the golang version or the set of volumes in the data
container). This will delete all older versions of images and containers when
the version is different.
* Rewrite a bunch of the hack/ directory with modular reusable bash libraries.
* Have 'build/*' build on 'hack/*'. The stuff in build now just runs hack/* in a docker container.
* Use a docker data container to enable faster incremental builds.
* Standardize output to _output/{local,dockerized}/bin/OS/ARCH/*. This regularized placement makes cross compilation work.
* Move travis specific scripts under hack/travis
With new dockerized incremental builds, I can do a no-op `make quick-release` in ~30s. This is a significant improvement.
Also a bunch of script clean up. Make make-clean.sh faster and more robust.
Building the docker run images and uploading to GCS are now optional and turned off by default. Doing a release shouldn't hit the network now (I think).
