The buzz surrounding Friday’s Millennium Stage performance was palpable, with the line forming hours ahead of time for a free concert that was part of the Kennedy Center’s outstanding Arabesque festival. The performer was K’Naan. Judging by the standing room crowd that filled the entire length of the Kennedy Center’s Grand Foyer, he stands on the cusp of being a “next big thing.” Judging by his energetic and thought provoking performance, his reputation is…