After her last decade in the Las Vegas heat, Celine Dion was ready for a change of scenery — the French-Canadian diva admitted it herself. Once Dion took the stage at the Barclays Center in Brooklyn on Friday, midway through her year-long, 120-date “Courage” tour, she gestured to her new surroundings, addressing 19,000 screaming fans (a mostly female group, some of whom came dressed for the occasion decked out in sparkling gowns).