LU-4315 doc: updating ls-tu man page style

LU-4315 doc: updating ls-tu man page style

Updating files to match the new code style for Lustre manual pages as
enforced by 'contrib/scripts/checkpatch-man.pl'.

This also includes other changes like removing < > or { } for singular
required arguments and placing [ ] around optional ones as well as
making all arguments CAPITAL and italicized, literal arguments are
bolded. Lines over 80 characters should be split at the natural line
end rather than the word that goes over the limit as fewer lines will
need to be modified when making changes if each sentence is on it's
own line.

Only using features that appear in groff 1.22.3 as this is the
available version is CentOS 8.

Checked files:
- lshowmount.8
- lustre.7
- lustreapi.7
- lustre_routes_config.8
- lustre_routes_conversion.8
- lustre_rsync.8
- mkfs.lustre.8
- mount.lustre.8
- mount.lustre_tgt.8
- nids.5
- plot-llstat.8
- routerstat.8
- tunefs.lustre.8

Test-Parameters: trivial
Signed-off-by: Frederick Dilger <fdilger@whamcloud.com>
Change-Id: Ib932b582273ef567b48e504af2d5437389330dd3
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56191
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>