On a sunny spring morning at the biggest book festival in the country, a slew of celebrities roll by on golf carts on the way to their morning sessions: Sarah Jessica Parker, Larry David, Lionel Richie are among the headliners at the Los Angeles Times Festival of Books … and then there is the most popular face of all. “Valerie! Valerie!” they scream — and why not? Fans have known her since she was 15 in the now-iconic role of Barbara Cooper on the hit sitcom “One Day at a Time.” Valerie Bertinelli, who turned 66 on April 23, has gone from actor to inspiration. Her new book is “Getting Naked: The Quiet Work of Becoming Perfectly Imperfect.” It’s a self-help guide wrapped up in a skin-shedding personal memoir that focuses on acceptance, healing from trauma and letting go of the need to be perfect. “It’s uncomfortably personal,” Bertinelli says with a wide smile. “It’s about getting naked with who I am, emotionally and physically.…