The disappearance of China's Defence Minister Li Shangfu, who is being investigated for corruption, is just the latest recent case in which a senior official in President Xi Jinping's entourage has mysteriously vanished. The disappearance is often the first discernible sign that an official has come under investigation by the feared Central Commission for Discipline Inspection - a watchdog under the Chinese Communist Party tasked with policing officials suspected of violating party regulations o