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Write marshalled kubeletconfig object to init-config-dir
**What this PR does / why we need it**:
from @luxas :
>Write the the marshalled kubeletconfig object to /var/lib/kubelet/config/init/kubelet so that the kubelet will start up with the right params on init/join. The only params expected in the kubelet command-line after this is kubelet --init-config-dir /var/lib/kubelet/config/init --dynamic-config-dir /var/lib/kubelet/config/dynamic
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
ref: https://github.com/kubernetes/kubeadm/issues/28#issuecomment-345502933
**Special notes for your reviewer**:
/cc @kubernetes/sig-cluster-lifecycle-pr-reviews
**Release note**:
```release-note
NONE
```