CG APIs work as follows:
* Create CG - Create only in groups table
* Modify CG - Modify in CG table if CG in CG table, otherwise modify
in groups table.
* Delete CG - Delete from CG or groups table depending on where it is
* List CG - Check both CG and groups tables
* List CG snapshots - Check both CG and groups tables
* Show CG - Check both tables
* Show CG snapshot - Check both tables
* Create CG snapshot - Create either in CG or groups table depending on
the CG.
* Create CG from source - Create in either CG or groups table
depending on the source.
* Create volume - Add volume either to CG or group
Additional notes:
* default_cgsnapshot_type is reserved for migrating CGs.
* Group APIs will only write/read in/from the groups table.
* Group APIs won't work on groups with default_cgsnapshot_type.
* Groups with default_cgsnapshot_type can only be operated by CG APIs.
* After CG tables are removed, we'll allow default_cgsnapshot_type
to be used by group APIs.
Partial-Implements: blueprint generic-volume-group
Change-Id: Idd88a5c9587023a56231de42ce59d672e9600770
