(AFP) – “Grey rhinos” have become a hunted species in China, where government regulators are clamping down on powerful private conglomerates amid fears they are racking up dangerous debt levels. Coined by an American policy analyst, the rhino reference points to long-visible threats that can charge suddenly and wreak havoc, as opposed to unforeseen “black swans”. In China, it refers in particular to four huge companies with diverse global empires: HNA (aviation, tourism, finance),…