By Elizabeth Piper, Alistair Smout and Andrew MacAskill LONDON (Reuters) – When Liz Truss was asked to come to parliament to explain the sacking of her good friend and finance minister, she sent Penny Mordaunt in her place, offering her potential successor a primetime opportunity to flex her political muscle. In what only underlined the dwindling fortunes of Truss, Mordaunt took the lead role on Monday to explain why her boss had sacked Kwasi Kwarteng and replaced him with former health minister Jeremy Hunt who ripped up much of her economic plan. “The prime minister is not under a desk,” Mord…