prefix module qualified names with __module__ (#23630)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23630
This is temporary, won't be needed with the new serialization format.
But for now, since the main module gets its name from the archive name,
we need this for safety, other wise something like
`torch.jit.save("torch.pt") will break things.
Test Plan: Imported from OSS
Reviewed By: jamesr66a
Differential Revision: D16592404
Pulled By: suo
fbshipit-source-id: b538dc3438a80ea7bca14d84591ecd63f4b1289f
