BEJUCAL, Cuba, June 14 (Reuters) – Just outside the sleepy Cuban village of Bejucal, a winding track, rutted with potholes and losing ground to the jungle, ends at a barbed wire fence. A sign warns: "KEEP OUT, MILITARY ZONE." What lies beyond remains largely a mystery, though the U.S. government has long suspected that China runs an intelligence gathering operation in this village that once hid Soviet nuclear warheads. A Reuters reporter traveled to Bejucal this week, gaining rare access to the area around the site that remains an enigma, even for locals, but that has come under scrutiny after…