'Add user to a tenant by creating a default role relationship.
:raises keystone.exception.ProjectNotFound: If the project doesn\'t
exist.
:raises keystone.exception.UserNotFound: If the user doesn\'t exist.'

def add_user_to_project(self, tenant_id, user_id):

    self.resource_api.get_project(tenant_id)
    self.ensure_default_role()
    self.driver.add_role_to_user_and_project(user_id, tenant_id, CONF.member_role_id)
    COMPUTED_ASSIGNMENTS_REGION.invalidate()
