Automatic merge from submit-queue (batch tested with PRs 53317, 52186). 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>.

Change default --cert-dir for kubelet to a non-transient location

The default kubelet `--cert-dir` location is `/var/run/kubernetes`, which is automatically erased on reboot on many platforms. As of 1.8.0, kubelet TLS bootstrapping and cert rotation now persist files in `--cert-dir`, this should default to a non-transient location. Default it to the `pki` subfolder of the default `--root-dir` Fixes #53288

Additionally, since `kubeadm` expects a running (albeit crashlooping) kubelet prior to running `kubeadm init` or `kubeadm join`, and was using the default `--root-dir` of `/var/lib/kubelet`, it should not expect that folder to be empty as a pre-init check. Fixes https://github.com/kubernetes/kubernetes/issues/53356

```release-note
kubelet: `--cert-dir` now defaults to `/var/lib/kubelet/pki`, in order to ensure bootstrapped and rotated certificates persist beyond a reboot.
```