Merge pull request #63626 from roycaihw/release-1.9

Automatic merge from submit-queue.

Manual cherrypick of kube-openapi changes for release-1.9

**What this PR does / why we need it**:
Cherry-picks https://github.com/kubernetes/kube-openapi/pull/64 and https://github.com/kubernetes/kube-openapi/pull/67
Fixes bugs that make apiserver panic when aggregating valid but not well formed OpenAPI spec (with empty `Paths`/`Definitions`)

**Release note**:

```release-note
Fixes bugs that make apiserver panic when aggregating valid but not well formed OpenAPI spec
```

/cc @mbohlool
/sig api-machinery

Kubernetes-commit: 8d48604c2eca912159636be258a5e68bfc4c6643
tree: dc8ca472f44ce735ba91183428a1791f0d16654d
  1. admission/
  2. admissionregistration/
  3. apps/
  4. authentication/
  5. authorization/
  6. autoscaling/
  7. batch/
  8. certificates/
  9. core/
  10. events/
  11. extensions/
  12. Godeps/
  13. imagepolicy/
  14. networking/
  15. policy/
  16. rbac/
  17. scheduling/
  18. settings/
  19. storage/
  20. LICENSE
  21. OWNERS
  22. README.md
README.md

This repo is still in the experimental stage. Shortly it will contain the schema of the API that are served by the Kubernetes apiserver.