Automatic merge from submit-queue (batch tested with PRs 55954, 56037, 55866, 55984, 54994). 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 kubeadm validation unit test coverage. **What this PR does / why we need it**: From: `ok k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/validation 0.100s coverage: 92.3% of statements` To: `ok k8s.io/kubernetes/cmd/kubeadm/app/apis/kubeadm/validation 0.114s coverage: 100.0% of statements` **Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*: Fixes # **Special notes for your reviewer**: /cc @luxas **Release note**: ```release-note NONE ```