NKANDLA, South Africa—Ignoring efforts to defuse a tense standoff, former South African President Jacob Zuma told hundreds of supporters gathered outside his rural estate that he is appealing his 15-month prison sentence and impending arrest by police. South Africa’s top court, the Constitutional Court, last week sentenced Zuma to prison for defying a court order that he should testify before a commission investigating allegations of rampant corruption when he was president from 2009 to 2018. Several witnesses, including former Cabinet ministers and top executives of state-owned corporations, have testified of Zuma’s wrongdoing, including allowing his associates, the Gupta family, to influence his Cabinet appointments and lucrative state contracts. Zuma did not turn himself in to authorities within five days, as the court ruling had ordered, and now faces arrest by police. Hundreds of Zuma’s supporters, including some who traveled more than 400 kilometers (250 miles), gathered outside Zuma’s sprawling Nkandla …