Automatic merge from submit-queue (batch tested with PRs 41342, 41257, 41295, 41367, 41230)
kubeadm: unit tests for apis/kubeadm/validation
**What this PR does / why we need it**: added tests to apis/kubeadm/validation pkg and raised coverage from ~21% to 100%.
Adding unit tests is a WIP from #34136
**Special notes for your reviewer**: /cc @luxas @pires
**Release note**:
```release-note
NONE
```
416c1a498e