A gasoline glut brought on by drivers buying less at filling stations is emerging as one of the biggest threats to the yearlong oil-price rally. U.S. gasoline consumption plummeted last month, nearly matching a 15-year low, government estimates show. It fell to as low as 8.2 million barrels a day, averaged over the four-week period ended Jan. 27. January sales at the pump fell 4.4% from a year ago, according to data from the…