Change stop watchdog log to verbose info

[DavidXU12345]

When running test, stopping log for watchdog spams the test log, let's make it verbose level 4 so that it won't show during test.

Is this a bug fix or adding new feature?
Minor change

What is this PR about? / Why do we need it?
the watchdog stopping... log makes it difficult to read the test log, let's make it klog.V(4).Info so that it won't be printed out during test

What testing is done?
N/A

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: DavidXU12345
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[k8s-ci-robot]

Hi @DavidXU12345. 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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