Add labels to ml-engine job (#1361)
Add labels to ml-engine job (#1361)

Cloud ML Engine can use [labels](
https://cloud.google.com/ml-engine/docs/tensorflow/resource-labels) to organize and filter jobs. This PR adds labels for `model`, `problem` and `hparams_set`.
tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor