List all block volumes

def volume_list(self, search_opts=None):
        '''
        List all block volumes
        '''
        if self.volume_conn is None:
            raise SaltCloudSystemExit('No cinder endpoint available')
        nt_ks = self.volume_conn
        volumes = nt_ks.volumes.list(search_opts=search_opts)
        response = {}
        for volume in volumes:
            response[volume.display_name] = {
                'name': volume.display_name,
                'size': volume.size,
                'id': volume.id,
                'description': volume.display_description,
                'attachments': volume.attachments,
                'status': volume.status
            }
        return response