Convert volume_type id from int to uuid.

Convert volume_type id from int to uuid.

This converts the volume_type id from int to uuid.  In
addition, this also corrects an issue of deleting volume_types
by name.  Even though the client/api is taking the id, it was
converting to the name of the volume_type for the db access.

We also want to continue enforcing that the name is unique on creation
so as to avoid any confusion and for clarity in Horizon.  The api
has also been enhanced to allow you to specify the type by name
or by uuid.

This does NOT modify the things like the volume details display field
(currently shows the type 'name' not 'uuid'), these types of changes
will go in to V2 of the API.

Implements blueprint vol-type-to-uuid

Change-Id: I1c54ff2a1e0c5df5891408fc11b15176db4028c3