“ Whenever, because of a public exigency directly connected with the national-defense program, or because of the urgency for the immediate filling of a position involved in such program, the Civil Service Commission determines that it is in the public interest to do so, it may authorize the filling of any position connected with the national-defense program for a term not extending beyond the duration of the national-defense program, without regard to the competitive requirements of the Civil Service Rules, subject to such noncompetitive tests of fitness as the Commission may prescribe. ”