LU-16445 sec: make nodemap root squash independent of map_mode

LU-16445 sec: make nodemap root squash independent of map_mode

When the admin property is set to 0 on a nodemap, the root user must
be squashed, even if the map_mode property specifies to not map uids
or gids.

Enhance sanity-sec test_17 to exercise this use case.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I1b41caa1ccc6e544ce9fac45b47d0c4c129221f7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49561
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Etienne AUJAMES <eaujames@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>