**What this PR does / why we need it**:
Makes functions in validation/schema.go private to kubectl,
further isolating kubectl.
**Which issue this PR fixes**
Part of a series of PRs to address kubernetes/community#598
**Release note**:
```release-note
NONE
```
Part of #108.
Also:
* Added hyperkube cmd (not built by default yet).
* Added version support to hyperkube
* Remove health_check_minions flag from apiserver as it is no longer used with #3733
This is the start of an uber-binary that can morph into any server. Eventually we'll want this to be able to launch multiple servers from a single command line.