Lists all registered GRR users.

def ListGrrUsers(self):
    """Lists all registered GRR users."""

    args = user_management_pb2.ApiListGrrUsersArgs()

    items = self._context.SendIteratorRequest("ListGrrUsers", args)
    return utils.MapItemsIterator(
        lambda data: GrrUser(data=data, context=self._context), items)