Modifies user's type and/or password.

def Modify(self, user_type=None, password=None):
    """Modifies user's type and/or password."""

    args = user_management_pb2.ApiModifyGrrUserArgs(
        username=self.username, user_type=user_type)

    if user_type is not None:
      args.user_type = user_type

    if password is not None:
      args.password = password

    data = self._context.SendRequest("ModifyGrrUser", args)
    return GrrUser(data=data, context=self._context)