Merge pull request #12551 from nathanielmanistaatgoogle/grpc_1_0_flag

grpc_1_0 flag for gRPC Python Protoc Plug-In.

src/compiler/python_generator.cc

@@ -769,7 +769,7 @@ bool PythonGrpcGenerator::Generate(const FileDescriptor* file,
   PrivateGenerator generator(config_, &pbfile);
   if (parameter == "grpc_2_0") {
     return GenerateGrpc(context, generator, pb2_grpc_file_name, true);
-  } else if (parameter == "") {
+  } else if (parameter == "grpc_1_0" || parameter == "") {
     return GenerateGrpc(context, generator, pb2_grpc_file_name, true) &&
            GenerateGrpc(context, generator, pb2_file_name, false);
   } else {