If an agreement or provision for arbitration provides a method for the appointment of arbitrators this method shall be followed. In the absence thereof, or if the agreed method fails or for any reason cannot be followed, or if an arbitrator who has been appointed fails or is unable to act and his successor has not been duly appointed, the court, on application of a party to such agreement or provision, shall appoint one or more arbitrators. An arbitrator so appointed shall have the same powers as if he had been named or provided for in the agreement or provision.