Add a success message to verify-boilerplate

[markmc]

I fooled myself into thinking this wasn't actually doing anything, so I figure it would be good to add a reassuring success message:

$ ./hack/verify-boilerplate.sh
Verified 111 file headers match boilerplate

It's arguable this change should go into k/k first, but perhaps a little laziness can be forgiven!

/kind cleanup

[k8s-ci-robot]

Hi @markmc. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[robscott]

Thanks @markmc!

/ok-to-test
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: markmc, robscott

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