message: hot restart: start parent shutdown sequence after init complete
  Previously it was possible to race with initialization.
diff: @@ -187,7 +187,6 @@ void InstanceImpl::initialize(Options& options, TestHooks& hooks,
  HotRestart::ShutdownParentAdminInfo info;
  info.original_start_time_ = original_start_time_;
  restarter_.shutdownParentAdmin(info);
  - drain_manager_->startParentShutdownSequence();
  original_start_time_ = info.original_start_time_;
  admin_.reset(new AdminImpl(initial_config.admin().accessLogPath(),
  initial_config.admin().profilePath(), initial_config.admin().address(),
  @@ -297,6 +296,7 @@ void InstanceImpl::startWorkers(TestHooks& hooks) {
  // At this point we are ready to take traffic and all listening ports are up. Notify our parent
  // if applicable that they can stop listening and drain.
  restarter_.drainParentListeners();
  + drain_manager_->startParentShutdownSequence();
  hooks.onServerInitialized();
  }
  