Build an appropriate error message from a given option and
    a list of expected values.

def _error_msg_routes(iface, option, expected):
    '''
    Build an appropriate error message from a given option and
    a list of expected values.
    '''
    msg = 'Invalid option -- Route interface: {0}, Option: {1}, Expected: [{2}]'
    return msg.format(iface, option, expected)