Use log.warning() instead of log.warn() in oslo.db

Method warn() is provided by ContextAdapter from openstack common log
module. It is the same as logging.LoggerAdapter.warning(), so we can
easily replece it to warning().

It allows us drop dependency on log module from oslo db code.

Change-Id: I31fe047a8c71b2818c81dd6aa9cef96026c9b649
Typos fix in db and periodic_task module

Fix several typos in db/sqlalchemy/models.py and periodic_task.py

Change-Id: I7a4e72ee379f650192e656fe260d858fecea4637
Merge "Use log.warning() instead of log.warn() in oslo.db"
Merge "Typos fix in db and periodic_task module"