LU-18081 tests: improve conf-sanity/98 testing

LU-18081 tests: improve conf-sanity/98 testing

conf-sanity test_98 is failing for newer distros like Ubuntu 24.04
and SLES15sp6, which have newer userspace tools.

Print better error messages about what options are being processed
to help debug this issue.  It appears mount is now deduplicating
options passed on the command-line, which invalidates the test case.

Change test_98 to call mount.lustre directly to verify this handling.

Lustre-change: https://review.whamcloud.com/55891
Lustre-commit: ae475331db533826fe444a71bf61ad08d42c0a21

Test-Parameters: trivial
Test-Parameters: testlist=conf-sanity env=ONLY=98 clientdistro=sles15sp6
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I34de0fdbd4ca36228d313b53251b5dbcfc502b07
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59433
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Frederick Dilger <fdilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>