With people fighting to earn Foursquare badges by checking in to their apartment buildings and other mundane locations every day, it’s hard to remember that we do not live in a video game where our sole purpose is to make it to the next level. In a whimsical and truly playful turn, Salman Rushdie stabs at our desire to collect magic mushrooms through the eyes of a 12-year-old protagonist in “Luka and the Fire of Life.”