LU-2829 tests: decrease load on zfs for sanityn/33a-b

LU-2829 tests: decrease load on zfs for sanityn/33a-b

This patch decreases the number of files again for sanityn
test 33a and 33b based on the following patch:

Lustre-commit: 41ba272d1904bb9c612f785f608fc2d396763581
Lustre-change: http://review.whamcloud.com/8273

Test-Parameters: envdefinitions=SLOW=yes \
mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs \
ostcount=2 testlist=sanityn

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: Ia768d13b8db174e46ecc284433989a17cd560d07
Reviewed-on: http://review.whamcloud.com/8439
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>