Sync some db changes from Oslo

Import two new db exception classes, and
sync many changes to openstack.common.db.sqlalchemy:
- models.py has better py3 support
- updated / deprecated option names in session.py
- many new functions available in utils.py

Change-Id: Ia7bac4ea61dbb8cb5baf6cf2064a94895cba3f2c
Merge "Sync some db changes from Oslo"