An audition for the next bubbly Rachael Ray or earthy Emeril Lagasse would be rowdy, right? You'd think the personalities would be bouncing off the walls as chefs rumbled over who made the best coq au vin. But yesterday's atmosphere at the Flat Iron Tapas Bar & Lounge at the Bulfinch Hotel was tense and quiet, almost like a classroom in which students wait to take the SAT. The Next Food Network Star had......