Set default log level of loopingcall module to 'INFO'

Because we introduced oslo_service.loopingcall module in Mistral, just as
the oslo_service.periodic module, we should set the default log level to
'INFO' to avoid annoying logs.

Change-Id: If13139910fcb58c03fce845b03af338f82f87af3

mistral/config.py

@@ -120,6 +120,7 @@ _DEFAULT_LOG_LEVELS = [
     'eventlet.wsgi.server=WARN',
     'stevedore=INFO',
     'oslo_service.periodic_task=INFO',
+    'oslo_service.loopingcall=INFO',
     'mistral.services.periodic=INFO'
 ]