What is the problem?

Ray version and other system information (Python version, TensorFlow version, OS): 0.9dev

When multiple raylets are started locally, it used to be that they would each log to a separate file, e.g., raylet.1.out, raylet.2.out, etc. Now, they all log to raylet.out, which makes it harder to debug.

Reproduction (REQUIRED)

Any checked in pytest that starts a local cluster. For example, RAY_BACKEND_LOG_LEVEL=debug pytest -sv python/ray/tests/test_advanced.py::test_wait_cluster

• I have verified my script runs in a clean environment and reproduces the issue.
• I have verified the issue also occurs with the latest wheels.