multi: add shutdown logs in subservers

This commit adds a simple shutdown to every subserver to assist
debugging.

netann/host_ann.go

@@ -68,6 +68,7 @@ func (h *HostAnnouncer) Start() error {
 // Stop signals the HostAnnouncer for a graceful stop.
 func (h *HostAnnouncer) Stop() error {
 	h.stopOnce.Do(func() {
+		log.Info("HostAnnouncer shutting down")
 		close(h.quit)
 		h.wg.Wait()
 	})