LU-8585 test: fix sanity/200 looping breakage

LU-8585 test: fix sanity/200 looping breakage

Create test files in $tdir instead of another directory name
so that run_one_logged() will cleanup the test files after
each iteration when run in a loop.

Change-Id: I9bf8a74990a3ebe65b8d42a55d52a03072b02728
Test-Parameters: trivial testlist=sanity env=ONLY=200,ONLY_REPEAT=250
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/57576
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>