make cudnn rnn respect current stream (#27026)
Summary:
Make cudnn rnn respect current stream. After this lands, non-default test stream can be reenabled in https://github.com/pytorch/pytorch/issues/26791
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27026
Test Plan: default stream functionality is tested in existing tests, stream safety tests will be added in https://github.com/pytorch/pytorch/issues/26791
Differential Revision: D17656967
Pulled By: ngimel
fbshipit-source-id: 8b051aedd1df089b21f666ec553a5acefffdac88
