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
}