'Update an image.
For a full list of available parameters, please refer to the official
API reference:
http://developer.openstack.org/api-ref/image/v2/index.html#update-an-image'

def update_image(self, image_id, patch):

    data = json.dumps(patch)
    headers = {'Content-Type': 'application/openstack-images-v2.0-json-patch'}
    (resp, body) = self.patch(('images/%s' % image_id), data, headers)
    self.expected_success(200, resp.status)
    body = json.loads(body)
    return rest_client.ResponseBody(resp, body)
