Sync db.sqlalchemy from oslo-incubator

This updates db.sqlalchemy from oslo-incubator from hash
6f3e5a57aea5402031c4cc8863e0e35f7f222794

 $ python update.py --nodeps --base keystone \
    --dest-dir ../keystone --modules db.sqlalchemy

Change-Id: I2c8c104b6116f3f0cf0f17df196924ab7c20e072
Merge "Sync db.sqlalchemy from oslo-incubator"