LU-9727 lustre: add uid/gid to Changelogs entries

LU-9727 lustre: add uid/gid to Changelogs entries

Add a new changelog extension named changelog_ext_uidgid to hold
uid/gid information.
uid/gid info is added to every Changelog entry type except MARK, in
the form 'u=<uid>:<gid>':
5 01CREAT 15:44:32.385864793 2017.07.18 0x0 t=[0x200000402:0x3:0x0]
ef=0x1 u=500:500 p=[0x200000402:0x2:0x0] file1

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ie09e4cd146dea75985de00b1da58f75c2a5928f2
Reviewed-on: https://review.whamcloud.com/28114
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>