Make sure oattr cache fails when not all values are available.
Make sure oattr cache fails when not all values are available.

Because attributes are stored by value we may have a subset of the
attributes we want available. By using a LEFT JOIN we get rows with
a NULL value when we cannot find the data for some attributes.

cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond,cmusatyalab/opendiamond