Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
Duplicate a constant - LabelNodeRoleMaster
**What this PR does / why we need it**:
Per request from @luxas in 53458, to avoid cmd/kubeadm to
depend on pkg/controller/service. Added a comment to make
this clear.
**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**:
**Release note**:
```release-note
NONE
```
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