By Robin Emmott, Tom Balmforth and Vladimir Soldatkin BRUSSELS/MOSCOW (Reuters) -Britain said on Thursday the “most dangerous moment” in the West’s standoff with Moscow appeared imminent, as Russia held military exercises in Belarus and the Black Sea following its military buildup near Ukraine. Ukraine also staged war games and a senior U.S. official warned that “bodybags will come back to Moscow” if Russian troops crossed the border. But leaders on all sides signalled they hoped diplomacy could still prevail in what British Prime Minister Boris Johnson called Europe’s biggest security crisis …