By Duncan Miriri and Ayenat Mersie NAIROBI (Reuters) -Kenyans voted in national elections on Tuesday, but turnout was unusually low amid voter apathy and frustration over surging food prices, corruption and fears of violence in some areas. Former political prisoner and veteran opposition leader Raila Odinga is competing with Deputy President William Ruto for the presidency. Kenyans will also vote for legislators and local officials. Provisional results started streaming in on Tuesday night, but official announcements will take longer. Nic Cheeseman, professor of democracy at the University of …