Ernest Hemingway left Cuba shortly after Fidel Castro’s revolution, as relations with the United States began to fall into a deep freeze. Over five decades later, the author of “The Old Man and the Sea” returns to the island thanks to the magic of the silver screen.“Papa: Hemingway in Cuba” opens today in U.S. theaters as the first full-length Hollywood feature filmed on the island since the 1959 Cuban Revolution, having wrapped even before Havana and Washington’s historic announcement …