Script module data parallel (#16891)
Summary:
support data parallel for ScriptModule.
see unit tests for testing done for this PR. I also tried traced version of resnet18 from torchvision.
I'm yet to try a complete end-to-end data parallel training. This will be next steps.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16891
Differential Revision: D14002222
Pulled By: gqchen
fbshipit-source-id: fce3598169113215599815c6978e66d3c3a8c282
