El Segundo’s Chris Pimentel may be California’s happiest mayor. As his counterparts in Los Angeles , San Jose and San Francisco struggle with budgetary nightmares, Pimentel has at his disposal rising revenues, a booming job market and an energetic business community. The reason: His small town of 17,000 south of LAX is the birthplace of SpaceX, and has emerged as the aerospace startup mecca in Southern California. “We try to reduce friction,” Pimentel, who served with the Marines in Iraq,