Force kubectl to the git repo version if we detect a built version.
Add a KUBECTL_PATH override so that system/home directory versions of
kubectl can be used if desired. Remove existing $HOME inference.
Also fix up cert generation. It was failing during the first salt highstate when trying to chown the certs as the apiserver user didn't exist yet. Fix this by creating a 'kube-cert' group and chgrping the files to that. Then make the apiserver a member of that group.
Fixes#2365Fixes#2368
* 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.
