Must check if rule actually exists before proceeding with load.

def _load(self, **kwargs):
        """Must check if rule actually exists before proceeding with load."""

        if self._check_existence_by_collection(
                self._meta_data['container'], kwargs['name']):
            return super(Rules, self)._load(**kwargs)
        msg = 'The rule named, {}, does not exist on the device.'.format(
            kwargs['name'])
        raise NonExtantPolicyRule(msg)