Helper function to turn a name into an arn string,
    returns None if not able to resolve

def _get_role_arn(name, **conn_params):
    '''
    Helper function to turn a name into an arn string,
    returns None if not able to resolve
    '''
    if name.startswith('arn:aws:iam'):
        return name
    role = __salt__['boto_iam.describe_role'](name, **conn_params)
    rolearn = role.get('arn') if role else None

    return rolearn