Use oslo.db library

oslo.db library has been graduated from oslo-incubator,
so now we can use it instead of ironic.openstack.common.db.* code.

Co-Authored-By: Ghe Rivero <ghe.rivero@hp.com>

Implements: blueprint oslo.db

Change-Id: I250050a7dbd8735ba3af954223b54eabae793f59
Merge "Use oslo.db library"