Add --no_python flag (#29144)
Summary:
Allows you to use a bash script wrapper in-between launch and your
training script. e.g.
```
python -m torch.distributed.launch --nproc_per_node=8 --no_python --use_env \
bash -c 'exec numactl --cpunodebind=$(( LOCAL_RANK / 4 )) "$@"' -- \
python train.py ...
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29144
Differential Revision: D18345647
Pulled By: pietern
fbshipit-source-id: f05849c38c82de782988d07d300e00cf9f37253a
