Automatic merge from submit-queue
kubeadm: Upload configuration used at 'kubeadm init' time to ConfigMap for easier upgrades
**What this PR does / why we need it**:
Uploads config used to a ConfigMap so we can upgrade a cluster seamlessly without forcing the user to re-specify all options they specified the first time.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
fixes: https://github.com/kubernetes/kubeadm/issues/373
**Special notes for your reviewer**:
This should be a cherrypick-candidate for easier upgrading to v1.8
cc @wojtek-t
**Release note**:
```release-note
kubeadm: Upload configuration used at 'kubeadm init' time to ConfigMap for easier upgrades
```
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