By Michael Noble Jr. TULSA, Okla. (Reuters) – A man who fatally shot five people including himself at an Oklahoma medical building, after buying an assault-style rifle on the same day, had gone there to kill a doctor who he blamed for back pain he felt after surgery, authorities said on Thursday. The suspect, identified as Michael Louis, entered a building on Tulsa’s St. Francis Health System campus with a semi-automatic weapon on Wednesday and opened fire at anyone he encountered, Tulsa Police Chief Wendell Franklin said at a news briefing. Two doctors, a receptionist and a patient were kille…