By Davide Barbuscia and Suzanne McGee NEW YORK (Reuters) -Investors look set to face a volatile few months ahead after the Federal Reserve resumed interest rate cuts and opened the door to further easing but tempered its message with warnings of sticky inflation, sowing doubt over the pace of future policy adjustments. Some investors are now less certain that a rapid shift to lower borrowing costs will materialize, potentially dampening optimism that stocks and bonds would get a strong lift from easier p ...