LU-7192 tests: conf-sanity test 32c supports DNE on ZFS

LU-7192 tests: conf-sanity test 32c supports DNE on ZFS

1. ZFS needs import pool before tunefs.
2. previous 2.4 ZFS disk image contains 100M file, which will cause
   'migrate' used up all OST space and fail, recreate the image.
3. generate test images for 2.7-formatted ldiskfs and zfs with
   DNE striped directories feature enabled and update t32_test()
   to test that.

Test-Parameters: alwaysuploadlogs envdefinitions=SLOW=yes,ENABLE_QUOTA=yes,ONLY=32 mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs mdtcount=4 testlist=conf-sanity
Change-Id: Ib35e4cb80d6beee9695b26844c4e6a99e88adb89
Signed-off-by: Lai Siyao <lai.siyao@intel.com>
Signed-off-by: Jian Yu <jian.yu@intel.com>
Reviewed-on: http://review.whamcloud.com/16663
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>