Update object metadata

        :param container: container name (Container is equivalent to
                          Bucket term in Amazon).
        :param obj: object name (Object is equivalent to
                    Key term in Amazon).
        :param metadata(dict): additional metadata to include in the request.

def update_object(self, container, obj, metadata, **kwargs):
        """Update object metadata

        :param container: container name (Container is equivalent to
                          Bucket term in Amazon).
        :param obj: object name (Object is equivalent to
                    Key term in Amazon).
        :param metadata(dict): additional metadata to include in the request.
        """
        try:
            LOG.debug('update_object() with %s is success.', self.driver)
            return self.driver.update_object(container, obj,
                                             metadata, **kwargs)
        except DriverException as e:
            LOG.exception('copy_object() with %s raised\
                            an exception %s.', self.driver, e)