Bug fix, blacklist image_summary metric for TPU.
Bug fix, blacklist image_summary metric for TPU.

PiperOrigin-RevId: 188768118

vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor,tensorflow/tensor2tensor,tensorflow/tensor2tensor,vthorsteinsson/tensor2tensor