Automatic merge from submit-queue (batch tested with PRs 49971, 51357, 51616, 51649, 51372)

kubectl: Remove ending punctuation from error strings

**What this PR does / why we need it**:

`golint` emits 2 warnings of type:

`error strings should not end with punctuation`

Remove punctuation from end of error strings.



**Release note**:

```release-note
NONE
```
/sig cli
/kind cleanup