Migrate block_device_mapping to use instance uuids.
Migrate block_device_mapping to use instance uuids.

This started out as wanting cleanup_volumes to take a UUID instead
of an instance ID, and ended up as a wander through the joys of
schema updates. I am assuming that we actually want to transition
these tables across to using the instance UUID instead of just the
ID.

This is my first attempt at a schema update, so please review this
patch with skepticism. Resolves bug 977975. Partially resolves
blueprint finish-uuid-conversion.

Change-Id: Ib5a6f8a872ea0530e201c70e9ac01cd14f82c557

n0ano/ganttclient