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>.
Improve validation of certificates. Fix bug in checking certificate validity
**What this PR does / why we need it**:
Improves the validation of dnsNames and commonNames on certificate resources.
Fixes a bug in checking certificate validity.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
Fixes#176, fixes#175
**Release note**:
```release-note
Fix a bug in checking certificate validity and improve validation of dnsNames and commonName
```
e32147b695