LU-2261 test: Re-enable sanity test 156 for zfs

LU-2261 test: Re-enable sanity test 156 for zfs

With the landing of LU-4259 zfs now supports brw
stats like ldiskfs. Earlier sanity test 156 was
disabled for zfs but now it can be re-enabled so
we can actually verify brw stats on zfs works.

Apply additional clean up to test 156: Spaces to tabs.

Change-Id: I0a0014bee4c666faadce96177c44953573d85ffd
Signed-off-by: James Simmons <uja.ornl@gmail.com>
Reviewed-on: http://review.whamcloud.com/13535
Tested-by: Jenkins
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>