Worker: sign off as last step of shutdown

Within the shutdown procedure, signing off is now the last thing the
worker does. This makes things more consistent from the Manager's point
of view (like receiving last-second log entries while the Worker is still
online).

cmd/flamenco-worker/main.go

@@ -144,14 +144,16 @@ func shutdown() {
 	done := make(chan struct{})
 	go func() {
 		if w != nil {
-			shutdownCtx, cancelFunc := context.WithTimeout(context.Background(), 3*time.Second)
-			defer cancelFunc()
-			w.SignOff(shutdownCtx)
 			w.Close()
 			listener.Wait()
 			if err := buffer.Close(); err != nil {
 				log.Error().Err(err).Msg("closing upstream task buffer")
 			}
+
+			// Sign off as the last step. Any flushes should happen while we're still signed on.
+			signoffCtx, cancelFunc := context.WithTimeout(context.Background(), 3*time.Second)
+			defer cancelFunc()
+			w.SignOff(signoffCtx)
 		}
 		close(done)
 	}()

internal/worker/worker.go

@@ -63,5 +63,4 @@ func (w *Worker) Close() {
 	log.Debug().Msg("worker gracefully shutting down")
 	close(w.doneChan)
 	w.doneWg.Wait()
-	log.Debug().Msg("worker shut down")
 }