The root cause for that error is because `rename` doesn't work
across different mount points.
The kubelet config file and back up directory are mounted to
different file system in kinder environment.
```
df /var/lib/kubelet/config.yaml | tail -n1 | awk '{print $1}'
/dev/sda2
df /etc/kubernetes/tmp/kubeadm-kubelet-configxxx | tail -n1 | awk '{print $1}'
overlay
```
Call `cp` instead of `rename` to back up the kubelet file would fix
that issue.
Signed-off-by: Dave Chen <dave.chen@arm.com>
c55a98fde9