Basic data parallel tests for ORTModule (#7812)
* Test Pytorch DDP with ORTModule
* Remove unused MP model
* Update orttraining/orttraining/test/python/orttraining_test_ort_module_pytorch_ddp.py
* Update orttraining/orttraining/test/python/orttraining_test_ort_module_pytorch_ddp.py
* Change file name
* Fix import
* Skip a test
* Address a comment
* Add test back
