In change-id Iabf9c3fab56ffef50695ce45745f193273822b39 we left the
`volume_attachment` out of the expected attributes of the Volume OVO
(even when te DB layer is providing that information) because it was
breaking some unit tests.
This means that in some cases we are unnecessarily loading the
attachments again (manually or via lazy loading) once we have the volume
OVO because that field is not set.
In this patch we populate the `volume_attachment` when we load the
Volume OVO from the DB.
Change-Id: I6576832b2c2722ab749cfe70bbc2058ead816c36
e07bf3787a