Hail, Caesar!, the new film by Joel and Ethan Coen, starts and ends with a confession and a slap in the face. The movie covers a day in the life of a production chief at Capitol Pictures, who is played by Josh Brolin. The Coens have named him Eddie Mannix, after a real Hollywood fixer who spent his career cleaning up the messy personal lives of MGM’s stars so that scandal would not hurt the box office. But Mannix’s confessions, which bracket Hail, are not the kind that turned up in the gossip…