* Pledge to ease political and social restrictions unfulfilled * President gambles on success of nuclear talks with West * But Rouhani leaves himself open to hardliners' attacks * U.N., activists alarmed by rise in executions By Babak Dehghanpisheh BEIRUT, Sept 25 (Reuters) - After a year in ******, Iranian President Hassan Rouhani has achieved a steady thaw in relations with the West but failed so far to deliver on campaign promises of more freedom at home. ...