'Updates the specified group.
For a full list of available parameters, please refer to the official
API reference:
https://developer.openstack.org/api-ref/block-storage/v3/#update-group'

def update_group(self, group_id, **kwargs):

    put_body = json.dumps({'group': kwargs})
    (resp, body) = self.put(('groups/%s' % group_id), put_body)
    self.expected_success(202, resp.status)
    return rest_client.ResponseBody(resp, body)
