'Update an existing user.
:param str user_id: User ID.
:param dict user: User modification. See user schema in
:class:`~.IdentityDriverBase`. Properties set to None will be
removed. Required properties cannot be removed.
:returns: user. See user schema in :class:`~.IdentityDriverBase`.
:raises keystone.exception.UserNotFound: If the user doesn\'t exist.
:raises keystone.exception.Conflict: If a duplicate user exists in the
same domain.'

@abc.abstractmethod
def update_user(self, user_id, user):

    raise exception.NotImplemented()
