The patch adds the following functionality:
* A default volume type (``__DEFAULT__``) will be
created during cinder DB migration.
* Admins can override the default type in cinder.conf
* Creating a new volume without any type (and
`default_volume_type` option is unset in cinder.conf)
will be assigned the ``__DEFAULT__`` type.
* The default volume type cannot be deleted
* All untyped volumes and snapshots will be migrated to the
``__DEFAULT__`` type.
Change-Id: I4da0c13b5b3f8174a30b8557f968d6b9e641b091
Implements: blueprint untyped-volumes-default-volume-type