message: Set gpu_options.allow_growth = true for c++ engine
diff: @@ -35,7 +35,10 @@ namespace minigo {
  TfDualNet::TfDualNet(const std::string& graph_path) {
  GraphDef graph_def;
  TF_CHECK_OK(ReadBinaryProto(Env::Default(), graph_path, &graph_def));
  - session_.reset(NewSession(SessionOptions()));
  +
  + SessionOptions options;
  + options.config.mutable_gpu_options()->set_allow_growth(true);
  + session_.reset(NewSession(options));
  TF_CHECK_OK(session_->Create(graph_def));
  inputs_.clear();
  