provide verbose output when health check fails

Kubernetes-commit: 3874e43550385c0f4adddc4ccbedf12478233692

pkg/server/healthz/healthz.go

@@ -181,6 +181,7 @@ func handleRootHealthz(checks ...HealthzChecker) http.HandlerFunc {
 		}
 		// always be verbose on failure
 		if failed {
+			klog.V(2).Infof("%vhealthz check failed", verboseOut.String())
 			http.Error(w, fmt.Sprintf("%vhealthz check failed", verboseOut.String()), http.StatusInternalServerError)
 			return
 		}