LU-4398 llite: do not cache write open lock for exec file

LU-4398 llite: do not cache write open lock for exec file

This is to avoid the problem that the MDT needs an extra lock
revocation to make the file be able to execute.

Signed-off-by: Jinshan Xiong <jinshan.xiong@uber.com>
Signed-off-by: Gu Zheng <gzheng@ddn.com>
Change-Id: Ibb42a9a8cb56a9bf48a6e972b72d3d71ed7fbaf5
Reviewed-on: https://review.whamcloud.com/32265
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>