fix import trainer_desc_pb2 error

test=develop

paddle/fluid/framework/trainer_desc.proto

@@ -39,7 +39,7 @@ message TrainerDesc {
   optional DataFeedDesc data_desc = 201;
 }
 
-message HogwildWorkerParameter {}
+message HogwildWorkerParameter { repeated string skip_ops = 1; }
 
 message DownpourWorkerParameter {
   repeated TableParameter sparse_table = 1;

python/paddle/fluid/trainer_desc.py

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from proto import trainer_desc_pb2
+from proto import trainer_desc_pb2 as trainer_desc_pb2
 from distributed import ps_pb2 as ps_pb2
 from device_worker import DeviceWorkerFactory
 from google.protobuf import text_format