[tune] Tune onto Logging Module (#2882)

Moves Tune onto logging in Python. Ignores examples and tests.

python/ray/tune/function_runner.py

@@ -2,14 +2,16 @@ from __future__ import absolute_import
 from __future__ import division
 from __future__ import print_function
 
+import logging
 import time
 import threading
-import traceback
 
 from ray.tune import TuneError
 from ray.tune.trainable import Trainable
 from ray.tune.result import TIMESTEPS_TOTAL
 
+logger = logging.getLogger(__name__)
+
 
 class StatusReporter(object):
     """Object passed into your main() that you can report status through.
@@ -74,7 +76,7 @@ class _RunnerThread(threading.Thread):
             self._entrypoint(*self._entrypoint_args)
         except Exception as e:
             self._status_reporter._error = e
-            print("Runner thread raised: {}".format(traceback.format_exc()))
+            logger.exception("Runner Thread raised error.")
             raise e
         finally:
             self._status_reporter._done = True