A Nigerian tomato paste plant said Thursday it is shutting down, firing 1,500 staff and moving abroad because it is unable to obtain the hard currency it needs to operate. The move is a public embarrassment for President Muhammadu Buhari and his plan to diversify the economy. Buhari, elected last year on a ticket to fix a country mismanaged for decades, frequently talks about ending the country’s dependency on oil exports by boosting local food production, repeating his mantra: “We must...