Rename test_distributed to test_distributed_fork (#42932)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42932
Follow up from https://github.com/pytorch/pytorch/pull/41769, rename `test_distributed` to `test_distributed_fork` to make it explicit that it forks.
New command to run test:
`python test/run_test.py -i distributed/test_distributed_fork -v`
ghstack-source-id: 111632568
Test Plan: `python test/run_test.py -i distributed/test_distributed_fork -v`
Reviewed By: izdeby
Differential Revision: D23072201
fbshipit-source-id: 48581688b6c5193a309e803c3de38e70be980872
