GitLab

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/309

Right now multiple machines can try to write to the same output file,
since they get the same argument. Additionally, on the same machine, several
outputs can be saved which requires unncessary unpacking. This change makes
train_net only write output of the rank 0 trainer.

Reviewed By: wat3rBro

Differential Revision: D37310084

fbshipit-source-id: 9d5352a274e8fb1d2043393b12896d402333c17b