LU-7584 tests: clean up sanity test_129

LU-7584 tests: clean up sanity test_129

Clean up sanity test_129 to follow Lustre script coding style.
There is no need to create so many files to verify that the
directory size limit has been removed.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ib80bd8a70386b3e8881f8ca3d417a8be1becab07
Reviewed-on: https://review.whamcloud.com/26874
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>