Run a single wandb instance per TPU run (#4851)
Run a single wandb instance per TPU run (#4851)

* Run a single wandb instance per TPU run

* wandb: self.is_world_master

* make style

Co-authored-by: Julien Chaumond <a2e75dc0f7a441a5f83dcee1a3f7492a8c3d1d78@gmail.com>
huggingface/pytorch-transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers,huggingface/transformers