Add unittests for jitting EMA model
Add unittests for jitting EMA model

Summary: As title

Reviewed By: nayansinghal

Differential Revision: D32005717

fbshipit-source-id: ebdf1ed0e4a2b9fccffd841d0fa7be0b50ec6b79

pytorch/fairseq,pytorch/fairseq,pytorch/fairseq