If the arbitration agreement provides a method of appointment of arbitrators, this method shall be followed. In the absence of a method of appointing, or if the agreed method fails or for any reason cannot be followed, or when an arbitrator appointed fails or is unable to act and a successor has not been appointed, the district court on application of a party shall appoint one or more arbitrators. An arbitrator appointed by the district court has the same powers as an arbitrator specifically named in the agreement.