“The absolute celebrational joy that’s going on at these shows is really something. But I’ve learned enough in life that these moments pass.” Photo: Jim Mitcham John Power feels like there’s a renaissance going on. He’s calling from London after performing two back-to-back nights at Wembley Stadium with his band, Cast, who were the chosen ones to open up for Oasis on their absolutely mad reunion tour . (Richard Ashcroft, of “Bitter Sweet Symphony” and the Verve fame, is the other.) “Yeah, I’m a