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
```
@kubernetes/sig-cluster-lifecycle-pr-reviews @timothysc