Automatic merge from submit-queue (batch tested with PRs 40796, 40878, 36033, 40838, 41210) kubeadm: added tests for preflight checks **What this PR does / why we need it**: There hadn't been much care to add more unit tests as more preflight checks were added. I added tests that increased coverage from ~9% to ~71% Adding unit tests is a WIP from https://github.com/kubernetes/kubernetes/issues/34136 **Special notes for your reviewer**: /cc @luxas @pires **Release note**: ```release-note NONE ```