MONTERREY, Mexico (Reuters) - A motel in northern Mexico is putting steel doors on its rooms to protect guests from kidnappings and shootings in an escalating war between rival drug cartels. Owners of the Rancho El Trueno, or Thunder Ranch, began fortifying the highway motel near Monterrey a year ago but have decided to shield all 35 rooms as drug killings have worsened in the area in recent months. Complete with hot tubs, red imitation-leather beds, mirrored walls and striptease poles, the rooms are shuttered behind steel gates about 1.5 inches (4 cm) thick and some already have steel doors....