'Deletes a group.
:param context: the context of the caller.
:param group: the group object.
:param volumes: a list of volume objects in the group.
:returns: model_update, volumes_model_update'

def delete_group(self, context, group, volumes):

    LOG.debug('Deleting    group.')
    if (not utils.is_group_a_cg_snapshot_type(group)):
        raise NotImplementedError()
    model_update = {'status': fields.GroupStatus.DELETED}
    volumes_model_update = []
    for volume in volumes:
        try:
            self._helpers.delete_vdisk(volume['name'], True)
            volumes_model_update.append({'id': volume['id'], 'status': 'deleted'})
        except exception.VolumeBackendAPIException as err:
            model_update['status'] = fields.GroupStatus.ERROR_DELETING
            LOG.error('Failed    to    delete    the    volume    %(vol)s    of    CG.    Exception:    %(exception)s.', {'vol': volume['name'], 'exception': err})
            volumes_model_update.append({'id': volume['id'], 'status': fields.GroupStatus.ERROR_DELETING})
    return (model_update, volumes_model_update)
