Scope a schema error to its policy name and resource.

def policy_error_scope(error, data):
    """Scope a schema error to its policy name and resource."""
    err_path = list(error.absolute_path)
    if err_path[0] != 'policies':
        return error
    pdata = data['policies'][err_path[1]]
    pdata.get('name', 'unknown')
    error.message = "Error on policy:{} resource:{}\n".format(
        pdata.get('name', 'unknown'), pdata.get('resource', 'unknown')) + error.message
    return error