ST. MORITZ, Switzerland — When most people think of the luxury alpine resort town of St. Moritz in Switzerland’s Engadin valley, they imagine serene log cabins, skiing that’s challenging for Olympians and heated pools overlooking one of the most pristine mountain ranges in the world. But for two days a year in February, the small town becomes a rumbling, gasoline-scented race venue for the ultrawealthy and their one-of-kind vintage cars.