BERLIN/ROME (Reuters) – Volkswagen’s own staff and one of its suppliers warned years ago about software designed to thwart emissions tests, two German newspapers reported on Sunday, as the automaker tries to uncover how long its executives knew about the cheating. The world’s biggest automaker is adding up the cost to its business and reputation of the biggest scandal in its 78-year history, having acknowledged installing software in diesel engines designed to hide their emissions of toxic gasses.