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kubectl should return an error if "-l" and "--all" are both specified
**What this PR does / why we need it**:
Per discussion in [#50497](https://github.com/kubernetes/kubernetes/pull/50497#discussion_r134881507)
**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**:
/assign @caesarxuchao @mengqiy
**Release note**:
```release-note
kubectl should return an error if "-l" and "--all" are both specified
```