EX-6692 tests: clean up test env in sanity-lipe-scan3.sh

EX-6692 tests: clean up test env in sanity-lipe-scan3.sh

This patch reformats the file system in sanity-lipe-scan3.sh
to clean up the test env before running subtests.

Test-Parameters: trivial testlist=sanity-lipe-scan3
Test-Parameters: trivial mdscount=2 mdtcount=4 \
testlist=sanity-lipe-scan3

Fixes: de1bb57641 ("EX-6170 tests: make sanity-lipe-scan3.sh support remote MDS")
Signed-off-by: Jian Yu <yujian@whamcloud.com>
Change-Id: I301149f7f585716fcb39ba9065c2f372fb075344
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/49621
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>