message: Improve gRPC error messages.
diff: @@ -1027,12 +1027,14 @@ REGISTER_TPU_DRIVER(
  ::grpc::Status status = stub->Open(&ctx, req, &resp);
  if (!status.ok()) {
  LOG(ERROR) << "Failed to open the gRPC driver: " << status.error_code()
  - << ": " << status.error_details();
  + << ": " << status.error_message() << ": "
  + << status.error_details();
  return xla::Status(
  tensorflow::error::Code(status.error_code()),
  absl::StrCat("Failed to connect to remote server at address: ",
  config.worker(),
  - ". Error from gRPC: ", status.error_details()));
  + ". Error from gRPC: ", status.error_message(),
  + ". Details: ", status.error_details()));
  }
  return std::unique_ptr<TpuDriver>(
  new GrpcTpuDriver(config, resp.client_id()));
  