CAMP LEATHERNECK, Afghanistan (Reuters) - U.S. Defence Secretary Leon Panetta arrived in Afghanistan on an unannounced visit on Wednesday, as the United States tried to contain fallout from a massacre of 16 Afghan civilians by an American soldier. A motorcycle bomb went off in Kandahar city in southern Afghanistan, killing an Afghan intelligence soldier and wounding two, as well as a civilian, while a roadside bomb killed 8 civilians in neighboring Helmand province, officials said, as Panetta kicked off a two-day trip by visiting troops. Panetta told them the weekend killings by what U.S. ...