LU-17224 tests: reduce MAXFREE in oos2.sh for ZFS

LU-17224 tests: reduce MAXFREE in oos2.sh for ZFS

If fallocate is unavailable on the OSTs, then do not run the
out-of-space test on large filesystems or it will time out.

Test-Parameters: trivial
Test-Parameters: testlist=sanityn env=ONLY=15 fstype=ldiskfs
Test-Parameters: testlist=sanityn env=ONLY=15 fstype=zfs
Fixes: dcd5f6c0a0 ("LU-17224 tests: improve OST out-of-space testing")
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I72bf52563522336a4689bbaa76984cf7e78e1ab8
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59105
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>