Can't configure nova to use MySQL as backend

Linux version: Ubuntu 12.10 server

root@openstack:/var/lib/nova# nova-manage version
2012.2 (2012.2-LOCALBRANCH:LOCALREVISION)

Even thou I have configured nova.conf to use MySQL:

root@openstack:/etc/nova# grep sql_connection nova.conf
sql_connection=mysql://root:password@localhost/nova

It still uses sqlite as the backend. I added these 2 lines to nova/db/sqlalchemy/session.py

def get_engine():
    """Return a SQLAlchemy engine."""
    global _ENGINE
    LOG.warn('-- Eduardo -- _ENGINE: %s', _ENGINE)
    LOG.warn('-- Eduardo -- sql_connection: %s', FLAGS.sql_connection)
    if _ENGINE is None:
        connection_dict = sqlalchemy.engine.url.make_url(FLAGS.sql_connection)

and obtain the following
2012-11-08 02:59:31 WARNING nova.db.sqlalchemy.session [-] -- Eduardo -- _ENGINE: Engine(sqlite:////var/lib/nova/nova.sqlite)
2012-11-08 02:59:31 WARNING nova.db.sqlalchemy.session [-] -- Eduardo -- sql_connection: sqlite:////var/lib/nova/nova.sqlite

confirming nova is using sqlite as the database.