Automatic merge from submit-queue (batch tested with PRs 41259, 41260)
kubeadm: changed manifest files to yaml
**What this PR does / why we need it**: Static Pods are currently stored as .json files in /etc/kubernetes/manifests. This PR instead writes them as YAML, as requested by the SIG.
**Which issue this PR fixes**: fixes #https://github.com/kubernetes/kubeadm/issues/153
**Special notes for your reviewer**: /cc @luxas
**Release note**:
```release-note
NONE
```
3f2a25e38a