[c10d] Use the term "errno" instead of "generic error" in logs and error messages (#71865)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71865
This PR changes the term "generic error" to "errno" in c10d log outputs and error messages to make the root cause more clear.
```
[W socket.cpp:634] The server socket on [localhost]:29501 is not yet listening (generic error: 111 - Connection refused), will retry.
```
becomes
```
[W socket.cpp:634] The server socket on [localhost]:29501 is not yet listening (errno: 111 - Connection refused), will retry.
```
ghstack-source-id: 147716733
Test Plan: No behavioral change, run existing unit and integration tests.
Reviewed By: H-Huang
Differential Revision: D33792822
fbshipit-source-id: f57b0ec0fc4135e83c46fdc93911edbce9d26ec1
(cherry picked from commit f61dd92a43b8e253b770c3db7da0a1fba9b81cab)
