By Greg Torode HONG KONG (Reuters) – Military analysts say a vessel spotted in a Chinese shipyard in rare, recent satellite images could be a new or upgraded class of nuclear-powered attack submarine. It is not clear whether the submarine is a new model, an upgrade of an existing vessel or something else. But diplomats and analysts have been watching closely after a Pentagon report in November said the Chinese navy was likely in the next few years to build a new attack submarine with vertical launch tubes for cruise missiles. Images obtained by Reuters from private satellite imagery provider P…