LU-18393 tests: $num_files should be multiple of $num_entries

LU-18393 tests: $num_files should be multiple of $num_entries

According to performance-sanity.sh test_4 failure
"md_validate_tests, items must be a multiple of items per directory",
set $num_files to be a multiple of $num_entries.

Test-Parameters: trivial testlist=performance-sanity
Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I8c635649ef016389d1bd22f8318a55f8d0f77962
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56785
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alex Deiter <adeiter@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>