By Akhtar Soomro and Asif Shahzad KARACHI, Pakistan (Reuters) -A suspected female suicide bomber killed three Chinese teachers in Karachi on Tuesday, police and officials said, in the first major attack this year against nationals of long-time ally China working in Pakistan. The three were among passengers on a minibus returning to Karachi university after a lunch break when the bomb exploded at the entrance to the university’s Confucius Institute, killing the Chinese teachers and a Pakistani national, police and officials said. A separatist group, the Baloch Liberation Army (BLA) based in sou…