Pop star Justin Bieber is already starting to act like a boy diva. Last week, the teen idol kept a student welcoming committee of fans, as well as cops, school officials and the press, waiting for more than an hour — because he diverted his motorcade to McDonald’s for an Egg McMuffin. Originally due to arrive at Long Beach Middle School at 8:30 a.m. last Friday for a 9:30 welcome and press conference before his performance in an auditorium full of tweenyboppers, Bieber didn’t show up until after 10. But his publicist, Melissa Victor, keeps denying he was late.