Automatic merge from submit-queue. 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>.

Autoset OpenAPI version w/o SecurityDefinitions

There's code to automatically populate OpenAPI info based on existing
generic apiserver config, but it only fires if securitydefinitions are
present.  This doesn't make much sense, since this info is both required
and independent of security definitions, and there's no easy, generic
way to generate security definitions for an aggregated API server.

**Release note**:
```release-note
Properly autopopulate OpenAPI version field without needing other OpenAPI fields present in generic API server code.
```