Fix socket timeout in test_data_parallel (#1522)

Summary:
Pull Request resolved: #1522

Example failure:
https://www.internalfb.com/intern/testinfra/testconsole/testrun/4785074873255877/
Passed and failed on rev 3c307b1e123f2007d69464836099b12fa4656423, so not due to a code change

Running locally at least, I see:
```
E0305 00:39:14.685009 1133092 socket.cpp:1019] [c10d] The client socket has timed out after 600000ms while trying to connect to (127.0.0.1, 29500).
```

Related thread: https://fb.workplace.com/groups/319878845696681/permalink/1241443370206886/

There's only one process in this test (`world_size=1`) so should be ok to use `localhost` instead of `127.0.0.1`

Reviewed By: cyrjano

Differential Revision: D70637306

fbshipit-source-id: 111bc966097dbcccfea57ee152edf4eb39c48179

Author: sarahtranfb

tests/attr/test_data_parallel.py

@@ -41,7 +41,7 @@
 """
 
 # Distributed Data Parallel env setup
-os.environ["MASTER_ADDR"] = "127.0.0.1"
+os.environ["MASTER_ADDR"] = "localhost"
 os.environ["MASTER_PORT"] = "29500"
 dist.init_process_group(backend="gloo", rank=0, world_size=1)