'Adds a tag on the resource.
For more information, please refer to the official API reference:
http://developer.openstack.org/api-ref/networking/v2/index.html#add-a-tag'

def create_tag(self, resource_type, resource_id, tag):

    uri = ('/%s/%s/tags/%s' % (resource_type, resource_id, tag))
    return self.update_resource(uri, json.dumps({}), expect_response_code=201, expect_empty_body=True)
