By Brian Thevenot NEW ORLEANS (Reuters) – Investigators in New Orleans were searching on Thursday for what motivated a U.S. Army veteran flying an ISIS flag from his truck to plow into a crowd of New Year’s revelers, killing 15 people and injuring 30 more before dying in a shootout with police. The probe was focused on whether the suspect, Shamsud-Din Jabbar, 42, a U.S. citizen from Texas who