Separate python logger module-wise (#2703)

## What do these changes do?
1. Separate the log related code to logger.py from services.py.
2. Allow users to modify logging formatter in `ray start`.

## Related issue number
https://github.com/ray-project/ray/pull/2664

python/ray/workers/default_worker.py

@@ -3,10 +3,12 @@ from __future__ import division
 from __future__ import print_function
 
 import argparse
+import logging
 import traceback
 
 import ray
 import ray.actor
+import ray.ray_constants as ray_constants
 
 parser = argparse.ArgumentParser(
     description=("Parse addresses for the worker "
@@ -38,6 +40,19 @@ parser.add_argument(
     help="the local scheduler's name")
 parser.add_argument(
     "--raylet-name", required=False, type=str, help="the raylet's name")
+parser.add_argument(
+    "--logging-level",
+    required=False,
+    type=str,
+    default=ray_constants.LOGGER_LEVEL,
+    choices=ray_constants.LOGGER_LEVEL_CHOICES,
+    help=ray_constants.LOGGER_LEVEL_HELP)
+parser.add_argument(
+    "--logging-format",
+    required=False,
+    type=str,
+    default=ray_constants.LOGGER_FORMAT,
+    help=ray_constants.LOGGER_FORMAT_HELP)
 
 if __name__ == "__main__":
     args = parser.parse_args()
@@ -51,6 +66,10 @@ if __name__ == "__main__":
         "raylet_socket_name": args.raylet_name
     }
 
+    logging.basicConfig(
+        level=logging.getLevelName(args.logging_level.upper()),
+        format=args.logging_format)
+
     ray.worker.connect(
         info, mode=ray.WORKER_MODE, use_raylet=(args.raylet_name is not None))