Automatic merge from submit-queue Don't blame DNS spec on Kubernetes requirement for lower-case DNS labels. **What this PR does / why we need it**: #39635 was rejected because it wasn't clear to the author (me) that lower-case DNS labels are in fact a [Kubernetes requirement](https://github.com/kubernetes/kubernetes/pull/39635#issuecomment-271404975) rather than from the [DNS RFC 1035](https://www.ietf.org/rfc/rfc1035.txt) or/and [DNS RFC 1123](https://www.ietf.org/rfc/rfc1123.txt). **Special notes for your reviewer**: @thockin this is a first pass to make the error messages clearer about the fact that DNS specs are not to _blame_.