LU-9727 lustre: implement CL_OPEN for Changelogs

LU-9727 lustre: implement CL_OPEN for Changelogs

Record OPEN events in Changelogs, and add a new changelog
extension named changelog_ext_openmode to hold open mode.
An OPEN changlog entry is in the form:
7 10OPEN  13:38:51.510728296 2017.07.25 0x242
t=[0x200000401:0x2:0x0] ef=0x7 u=500:500 nid=10.128.11.159@tcp m=-w-
By default, disable recording of OPEN events in Changelogs.
Note that CREAT are still recorded even if OPEN are disabled.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I72c479938ab4782523f1b16aef19fbbc96f43c7f
Reviewed-on: https://review.whamcloud.com/28214
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>