Automatic merge from submit-queue (batch tested with PRs 46787, 46876, 46621, 46907, 46819)
kubeadm: Only create bootstrap configmap if not exists.
**What this PR does / why we need it**:
The fact that this method was not idempotent was breaking kubeadm upgrades.
https://github.com/kubernetes/kubeadm/issues/278
**Release note**:
```release-note
NONE
```
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