BEIJING/HANOI, Sept 14 (Reuters) - Chinese defence minister Li Shangfu abruptly pulled out of a meeting with Vietnamese defence leaders last week, three officials with direct knowledge of the matter said, amid questions about his more than two-weeks-long absence from public view. Li, 65, was due to attend an annual gathering on defence cooperation hosted by Vietnam on its border with China on Sept. 7-8 but the meeting was postponed after Beijing told Hanoi days before the event that the minister had a "health condition," two Vietnamese officials said. The sudden postponement of the meeting and the reasons cited by...