Automatic merge from submit-queue (batch tested with PRs 46928, 47345)
kubeadm: Move directory ./master to ./phases/controlplane
**What this PR does / why we need it**:
- Moves app/master into phases/controlplane. It should be in the phases directory, was just overlooked earlier
- Harmonizes the import names in phases/controlplane with the similar import names in cmd/kubeadm
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
**Special notes for your reviewer**:
Please review only second and third commit, based on https://github.com/kubernetes/kubernetes/pull/47339
Targets v1.8
**Release note**:
```release-note
NONE
```
@kubernetes/sig-cluster-lifecycle-pr-reviews @timothysc @pipejakob
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