[torch/elastic] Revise distributed run script (#58159)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58159
This PR includes the following changes:
- The `--standalone` option of `torch.distributed.run` now uses the `c10d` backend instead of `etcd` backend.
- The `import` statement for `EtcdServer` has been removed from the run script.
- The docstrings and parameter descriptions of the run script have been revised and improved.
- The default port number of `EtcdRendezvousBackend` has been changed from 29500 to 29400 to improve the user experience when used along with the run script which uses the port 29500 for the distributed job store (a.k.a. `MASTER_PORT`) by default.
ghstack-source-id: 128782267
Test Plan:
- Run existing tests.
- Visually verified the correct rendering of the docs.
Reviewed By: tierex
Differential Revision: D28383681
fbshipit-source-id: a4098f7c23c97a2376a9c4023e81f82fedd04b10
