Make use of graduated oslo.log module

* use oslo.log for logging functionality
* get rid of the file /mistral/openstack/common/log.py

Implements: blueprint mistral-log-enhancement
Partial-Bug: #1459188

Change-Id: I6b62cffda0a20b6caf59cc30bcc33c21ae1e5898

mistral/workflow/base.py

@@ -17,8 +17,9 @@
 import abc
 import copy
 
+from oslo_log import log as logging
+
 from mistral import exceptions as exc
-from mistral.openstack.common import log as logging
 from mistral import utils as u
 from mistral.workbook import parser as spec_parser
 from mistral.workflow import commands