LU-14824 test: sanity 413a/b unlink timeout v2

LU-14824 test: sanity 413a/b unlink timeout v2

Unlinking remote/striped directories is slow on ZFS system, limit
total directory number for 1-stripe directory test in 413a/b on ZFS
system, and don't test striped directory to avoid timeout.

Also limit total stripe object count to avoid timeout.

Use fallocate to fill the MDTs if it is supported.  Add a new helper
function check_fallocate() that just determines if fallocate support
is available on the OST without trying to change the mode.  This is
cached across calls to avoid repeated SSH calls to get information
that is the same for the entire test run.

Test-Parameters: trivial
Test-Parameters: mdscount=2 mdtcount=4 fstype=ldiskfs testlist=sanity env=ONLY="413a 413b",ONLY_REPEAT=50
Test-Parameters: mdscount=2 mdtcount=4 fstype=zfs testlist=sanity env=ONLY="413a 413b",ONLY_REPEAT=50
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: Ie116e6df5aee3877ed9f093f58e7bd71f63ebbe5
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/49799
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>