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>.
use subtest for table units (pkg/kubectl)
**What this PR does / why we need it**:
Go 1.7 added the subtest feature which can make table-driven tests much easier to run and debug. Many table-driven tests in pkg/kubectl are not using this feature.
/kind cleanup
/area kubectl
Further reading: [Using Subtests and Sub-benchmarks](https://blog.golang.org/subtests)
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
NONE
```
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