Change LOG.warn to LOG.warning

Python 3 deprecated the logger.warn method, see:
https://docs.python.org/3/library/logging.html#logging.warning
so we prefer to use warning to avoid DeprecationWarning.

Change-Id: Ide5daf929e2e1717f6a756d609071ff329f443a8
Closes-Bug: #1508442

dracclient/resources/bios.py

@@ -545,8 +545,8 @@ class BIOSConfiguration(object):
                     invalid_attribs_msgs.append(validation_msg)
 
         if unchanged_attribs:
-            LOG.warn('Ignoring unchanged BIOS attributes: %r' %
-                     unchanged_attribs)
+            LOG.warning('Ignoring unchanged BIOS attributes: %r',
+                        unchanged_attribs)
 
         if invalid_attribs_msgs or read_only_keys:
             if read_only_keys: