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fix kubectl set resource/selector/subject output

**What this PR does / why we need it**:
kubectl set resource/selector/subject -o yaml doesn't return the expected format

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes https://github.com/kubernetes/kubectl/issues/51

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```