[RPC] Avoid polluting Python root logger on importing "torch" module (#34871)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34871
We used to configure root logger in RPC module. A stream handler is added to `root.handlers`. This is not desired behavior for pytorch users. We should instead keep the root logger handler list untouched.
We can configure the logger local to the rpc module, set it's log level, so it doesn't use it's ancestor, which is usually the root which has no stream handlers in most cases.
https://docs.python.org/3/library/logging.html#logging.Logger.setLevel
And add a stream handler to make it output to stdout, even if the root handlers is not configured and has an empty list.
https://docs.python.org/3/library/logging.html#logging.Logger.addHandler
https://docs.python.org/3/library/logging.handlers.html#logging.StreamHandler
ghstack-source-id: 100322141
Test Plan:
```
buck test mode/dev-nosan //caffe2/test/distributed/rpc:rpc_fork
buck build mode/dev-nosan //caffe2/test/distributed/rpc:rpc_fork \
&& buck-out/gen/caffe2/test/distributed/rpc/rpc_fork\#binary.par -r test_wait_all_workers
```
Differential Revision: D7677493
fbshipit-source-id: 88a66079e7348c79a7933e3527701917cbebb7ba
