Gov. Andrew M. Cuomo announced Monday at a news conference that the Islanders have agreed to a deal to evenly split their regular-season home games between Nassau Coliseum and Brooklyn’s Barclays Center in the years leading up to the opening of their new arena at Belmont Park. The Islanders’ first game at the Coliseum could be as early as September or October, Cuomo said. “The Islanders coming back to Long Island is like the cherry on the cake,” Cuomo said. Cuomo confirmed that the Islanders’ new arena at Belmont won’t be ready for three years.