do not flush if Write() failed (#13597)

- Go might reset the internal http.ResponseWriter() to `nil`
  after Write() failure if the go-routine has returned, do not
  flush() such scenarios and avoid spurious flushes() as
  returning handlers always flush.
- fix some racy tests with the console 
- avoid ticker leaks in certain situations

cmd/signals.go

@@ -66,8 +66,8 @@ func handleSignals() {
 			logger.LogIf(context.Background(), oerr)
 		}
 
-		if globalConsoleSrv != nil {
-			logger.LogIf(context.Background(), globalConsoleSrv.Shutdown())
+		if srv := newConsoleServerFn(); srv != nil {
+			logger.LogIf(context.Background(), srv.Shutdown())
 		}
 
 		return (err == nil && oerr == nil)