NEW YORK (Reuters) - Blackstone Group LP , the U.S. buyout firm which is relying on Saudi Arabia to provide half the money for its planned $40 billion infrastructure fund, waved off concerns about funding on Thursday even as controversy rages over the disappearance of a Saudi journalist that has frayed relations between Wall Street and the oil-rich kingdom.Blackstone Chief Executive Stephen Schwarzman pulled out this week from a planned investment conference in Saudi Arabia, following other Wall..