klog: logcheck: should not return error if no Go files are present

/kind bug

What steps did you take and what happened:

When running logcheck against a directory that contains no Go files, I get an error:

-: no Go files in /home/ehashman/src/k8s/_output/local/go/src/k8s.io/kubernetes/pkg/kubelet/volumemanager/reconciler/pods
logcheck: error during loading

What did you expect to happen:

I would expect a directory with no Go files to pass the linter.

Anything else you would like to add:

/cc @adisky /priority important-longterm