Creates a new GRR user of a given type with a given username/password.

def CreateGrrUser(self, username=None, user_type=None, password=None):
    """Creates a new GRR user of a given type with a given username/password."""

    if not username:
      raise ValueError("Username can't be empty.")

    args = user_management_pb2.ApiCreateGrrUserArgs(username=username)

    if user_type is not None:
      args.user_type = user_type

    if password is not None:
      args.password = password

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