message: Fixed possible data races. Since nebulaStore and raftpart share a thread pool (bgWorkers_),
  all raft services should to be stopped before bgWorkers_ was cleaned up.
diff: @@ -24,13 +24,13 @@ namespace kvstore {
  NebulaStore::~NebulaStore() {
  LOG(INFO) << "Cut off the relationship with meta client";
  options_.partMan_.reset();
  - bgWorkers_->stop();
  - bgWorkers_->wait();
  LOG(INFO) << "Stop the raft service...";
  raftService_->stop();
  LOG(INFO) << "Waiting for the raft service stop...";
  raftService_->waitUntilStop();
  spaces_.clear();
  + bgWorkers_->stop();
  + bgWorkers_->wait();
  LOG(INFO) << "~NebulaStore()";
  }
  