LU-16870 tests: Make 413a/b work on server 2.14 with client master

LU-16870 tests: Make 413a/b work on server 2.14 with client master

This patch makes 413a/b interop work on server 2.14
with client master.

First, this patch removes general redirect of cmd execution
(fallocate/dd) to dev/null from generate_uneven_mdts(). For
'dd' it might get little verbose however on failure it will
dump output to stdout giving more info.

Second, it adds check under check_fallocate_supported() to check
is fallocate is issued on MDS. If yes it check for version when
this feature was added. If not it falls back to 'dd' command

Third, under unload_modules() it check for version where
unload_modules_local() was added. If not it falls back to
non-unload_modules_local() version to unload module.

Test-Parameters: trivial testlist=sanity serverversion=2.14 env=ONLY=413a,413b,ONLY_REPEAT=10
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I8a8843dd32f7e88d6d0938b67ce24353c9f9cb65
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56768
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Deiter <adeiter@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>