By Nichola Groom, Cole Horton and Simon Jessop LOS ANGELES/NEW YORK, Aug 10 (Reuters) - For the first time, investors seeking to pour cash into U.S.clean energy projects can count on at least a decade of generous federal subsidies, offering them long-sought confidence in the staying power of the world´s third biggest renewables market. Tax credits for wind and solar projects have underpinned explosive...