make tensorflow logging to warning

bob/learn/tensorflow/__init__.py

+import logging
+logging.getLogger("tensorflow").setLevel(logging.WARNING)
+
+
 def get_config():
     """
     Returns a string containing the configuration information.
     """
     import bob.extension
-    return bob.extension.get_config(__name__)
\ No newline at end of file
+    return bob.extension.get_config(__name__)