'Derive the keystone userid, stored in the User resource_id.
Helper function to derive the keystone userid, which is stored in the
resource_id of the User associated with this key. We want to avoid
looking the name up via listing keystone users, as this requires admin
rights in keystone, so FnGetAtt which calls _secret_accesskey won\'t
work for normal non-admin users.'

def _get_user(self):

    return self.stack.resource_by_refid(self.properties[self.USER_NAME])
