func iamPolicyListVersions(arn string, iamconn *iam.IAM) ([]*iam.PolicyVersion, error) {
	request := &iam.ListPolicyVersionsInput{
		PolicyARN: aws.String(arn),
	}

	response, err := iamconn.ListPolicyVersions(request)
	if err != nil {
		return nil, fmt.Errorf("Error listing versions for IAM policy %s: %s", arn, err)
	}
	return response.Versions, nil
}