change default logger to dedicated one (#1064)

Fix test


Fix format

Update pytorch_lightning/__init__.py
Separate imports

pytorch_lightning/core/saving.py

@@ -1,9 +1,10 @@
 import csv
-import logging as log
 import os
 from argparse import Namespace
 from typing import Union, Dict, Any
 
+from pytorch_lightning import _logger as log
+
 
 class ModelIO(object):