Automatic merge from submit-queue (batch tested with PRs 62495, 63003, 62829, 62151, 62002). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Build cleanup with go 1.10
Simplify our build/test scripts now that go 1.10 is in play. It has caching that seems to actually work.
**Release note**:
```release-note
NONE
```
This will help avoid flakes when initializing WORKSPACE, since there are
two sources for each file. Any errors downloading or failed hashes cause
bazel to try the next url in the series.
**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
```
