JOHANNESBURG (Reuters) – Olusegun Obasanjo has had mixed results as a mediator of intractable conflicts across Africa since he stepped down as Nigeria’s president in 2007, although he has never tired of trying. But on Wednesday the 85-year-old secured a surprise win, leading the team that announced a cessation of hostilities in Ethiopia, marking a diplomatic breakthrough in a conflict that has killed thousands, displaced millions and left many starving. Aware that permanent progress in ending two years of fighting with roots that can be traced far further back in Ethiopia’s history, the former…