Comment 6 for bug 1427060

Per comment 4, we had some patches from Dan Smith at one point to create a uuid column in the block_device_mappings table and then use that in the objects, so we could avoid issues with bdm_update_or_create in the DB API. Those never landed because they were written for a latent boot from volume race with cells v1 and we decided to just not fix cells v1, but could still be useful for situations like this.