server: log when waiting for user goroutines on shutdown

Useful for debugging.

cmd/soju/main.go

@@ -335,7 +335,6 @@ func main() {
 				srv.SetConfig(serverCfg)
 			}
 		case syscall.SIGINT, syscall.SIGTERM:
-			log.Print("shutting down server")
 			srv.Shutdown()
 			return
 		}

server.go

@@ -343,6 +343,8 @@ func (s *Server) sendWebPush(ctx context.Context, sub *webpush.Subscription, vap
 }
 
 func (s *Server) Shutdown() {
+	s.Logger.Printf("shutting down server")
+
 	s.lock.Lock()
 	s.shutdown = true
 	for ln := range s.listeners {
@@ -355,6 +357,7 @@ func (s *Server) Shutdown() {
 	}
 	s.lock.Unlock()
 
+	s.Logger.Printf("waiting for users to finish")
 	s.stopWG.Wait()
 
 	if err := s.db.Close(); err != nil {