[testing] solve the port conflict
This is a fix for https://github.com/huggingface/transformers/pull/14331 which accidentally collapsed 2 distinct ports and the deepspeed tests started to fail.

Since `torch.dist` never releases the port, those tests that run emulated launcher env never release the port (but can re-use it). But then it prevents other tests that run with `python -m torch.distributed` to succeed and ending up with `Address already in use` error.

I'm going to merge this to unblock the CIs (ours and Deepspeed's) since tomorrow is a holiday, but would be happy to do a follow up PR if something can be improved.

@sgugger 
Thanks for fixing!