By Alistair Smout, Elizabeth Piper and Andrew MacAskill LONDON/KIGALI (Reuters) -Boris Johnson’s Conservatives lost two parliamentary seats on Friday, a crushing blow to the governing party that prompted the resignation of its chairman and intensified doubts about the future of Britain’s prime minister. In Rwanda for a meeting of Commonwealth nations, Johnson was defiant, pledging to listen to voters’ concerns and do more to tackle a cost-of-living crisis after what he described as “tough” results in the two so-called by-elections. The losses – one in the Conservatives’ traditional southern he…