harare retire army chief constantino chiwenga veteran politician kembo mohadi swear zimbabwe vice presidents thursday state-run zimbabwe broadcast corporation say wednesday pair appoint president emmerson mnangagwa elevate similar position rule zanu-pf party saturday chiwenga retire military month appointment expect reward lead de facto coup november end robert mugabe 37-year rule bring mnangagwa power also add sign consolidation power army since turn 93-year-old mugabe mnangagwa appoint several senior military officer cabinet rule party top decision-making body politburo mnangagwa pressure opposition party public implement political reform ex-army boss swear zimbabwe vice president thursday