Elton John strides purposively down a corridor dressed in what looks like devil costume for Liberace’s Halloween party. But he is not moving toward a stage or recording studio. He is not going to sing or compose. He is going to tell his story to a different kind of audience, a support group in a drug rehab facility. And to us.
“Rocketman,” produced by Sir Elton himself, is a sometimes-impressionistic retelling of…