Cleanup lint errors in the pkg/kubelet/server/... directory

[timstclair]

Cleanup some issues that were found while experimenting with https://github.com/alecthomas/gometalinter on the pkg/kubelet/server/... directories.

[yujuhong]

This is awesome! :-) What linters did you configure gometalinter to use?

/lgtm
/approve no-issue

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: timstclair, yujuhong

Associated issue requirement bypassed by: yujuhong

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[timstclair]

I used:

gometalinter --disable=errcheck --disable=golint --exclude=.*\.pb\.go k8s.io/kubernetes/pkg/kubelet/server/... | sort

We don't do a good job with doc comments, so golint outputs a ton of comments complaints. Errcheck looks for ignored errors, but when I went through the results, most of the cases seemed like legitimate places to ignore the errors. The linter also caught #48297, but I didn't want to fix it in this PR :)

[timstclair]

/test pull-kubernetes-e2e-gce-etcd3 issue #42086

[k8s-github-robot]

Automatic merge from submit-queue (batch tested with PRs 48317, 48313, 48351, 48357, 48115)