LU-10024 tests: sanity 120f restore stripe count option

LU-10024 tests: sanity 120f restore stripe count option

The patch for LU-3308 with commit ID c75aa6c74cd86c6 removed
the stripe count, '-c', input parameter for three calls to
test_mkdir in santiy test 120f. The stripe count parameter
should be restored so the test will work correctly.

Test-Parameters: trivial testgroup=review-dne-part-1
Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I33c98259c0ee7a209afa4e9002b3aa8cab42d55c
Reviewed-on: https://review.whamcloud.com/29204
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Gu Zheng <gzheng@ddn.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>