A jury yesterday convicted a Boston police officer of three counts of assault and battery on an Uber driver and of taking the man’s car without his permission during an alleged drunken, off-duty dust-up three years ago that Suffolk District Attorney Daniel F. Conley called “a slap in the face” to his honorable brethren in blue.Michael Colin Doherty, 43, who has been suspended from the force without pay since his arrest for the incident in South Boston, is scheduled to be sentenced April 17 by Suffolk Superior Court Judge Linda E.