LU-14645 tests: test lfs setdirstripe with '/$'

LU-14645 tests: test lfs setdirstripe with '/$'

This patch improves one of the lfs setdirstripe tests to
verify that dir name ending with '/' also works.

Lustre-change: https://review.whamcloud.com/49463
Lustre-commit: 4b9a39d3ed58a664a2498911ca1d3c9073c13bd3

Test-Parameters: trivial mdscount=2 mdtcount=4 \
env=ONLY=24B testlist=sanity

Change-Id: I237d5a9ebad42cc0569aa1db487d0df147372316
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49464
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>