Revert "Use oslo.db create_engine instead of SQLAlchemy"

This reverts commit b57d52aeb951bcfb9a2966ba7dc1b3f8b640bd8f.
Revert "Switch to using of oslo.db"

This reverts commit abd1b652f7168befe4345b5dcb59a95ca7fa2773.

Conflicts:
	neutron/db/api.py
	neutron/tests/unit/db/test_agent_db.py
	neutron/tests/unit/test_dhcp_rpc.py
	requirements.txt