There's only a [DEFAULT] section, but there should be a [database] section as well (not sure what else is missing)
For example:
# The SQLAlchemy connection string used to connect to the
# database (string value)
#connection=sqlite:////cinder/openstack/common/db/$sqlite_db
But according to ./cinder/openstack/common/db/sqlalchemy/session.py:
database_opts = [
cfg.StrOpt('connection',
default='sqlite:///' +
os.path.abspath(os.path.join(os.path.dirname(__file__),
'../', '$sqlite_db')),
help='The SQLAlchemy connection string used to connect to the '
'database',
deprecated_name='sql_connection',
deprecated_group=DEFAULT,
...
CONF.register_opts(database_opts, 'database')
So, either it's sql_connection in [DEFAULT] or connection in [database]
Everything in Cinder is currently listed under the "DEFAULT" section. Could pull the conf generation updates from common to fix it up to be more like Nova.