def keystone_configure_api_version(self, sentry_relation_pairs, deployment,
                                       api_version):
        """Configure preferred-api-version of keystone in deployment and
           monitor provided list of relation objects for propagation
           before returning to caller.

        :param sentry_relation_pairs: list of sentry, relation tuples used for
                                      monitoring propagation of relation data
        :param deployment: deployment to configure
        :param api_version: value preferred-api-version will be set to
        :returns: None if successful.  Raise on error.
        """
        self.log.debug("Setting keystone preferred-api-version: '{}'"
                       "".format(api_version))

        config = {'preferred-api-version': api_version}
        deployment.d.configure('keystone', config)
        deployment._auto_wait_for_status()
        self.keystone_wait_for_propagation(sentry_relation_pairs, api_version)
Configure preferred-api-version of keystone in deployment and
           monitor provided list of relation objects for propagation
           before returning to caller.

        :param sentry_relation_pairs: list of sentry, relation tuples used for
                                      monitoring propagation of relation data
        :param deployment: deployment to configure
        :param api_version: value preferred-api-version will be set to
        :returns: None if successful.  Raise on error.