* add object detection grpc client
Fixes: #377
* fix kubeflow-examples-presubmit error
object_detection_grpc_client.py depends on other files in
https://github.com/tensorflow/models.git, pylint will fail
for those files need to be compiled manually.
Since mnist_DDP.py has similar dependency, here just follow
mnist_DDP.py and ignore checking this file.
Hougang Liu