USC appointed a retired aerospace executive as interim president and laid out a detailed plan for selecting a permanent leader Tuesday, ending speculation about whether outgoing President C.L. Max Nikias might remain in the post.  Nikias, embattled over his administration’s handling of a campus gynecologist accused of sexually abusing patients, relinquished his duties after a meeting of USC’s board. The trustees tapped one of their own, Wanda Austin, an alumna and former president of the Aerospace Corp., to temporarily run the university.