LU-2230 tests: disable replay-dual test 21b with ZFS

LU-2230 tests: disable replay-dual test 21b with ZFS

This patch disables replay-dual test 21b with ZFS because
semantics of replay_barrier_nosync is different on ZFS:
spa_freeze() syncs all changes. IOW, "nosync" (which is
crucial here) doesn't work.

Test-Parameters: envdefinitions=SLOW=yes,ENABLE_QUOTA=yes \
mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs \
clientdistro=el6 serverdistro=el6 clientarch=x86_64 \
serverarch=x86_64 testlist=replay-dual

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I271839fa626bfb140bd077d895826c6b4539892f
Reviewed-on: http://review.whamcloud.com/7287
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Li Wei <wei.g.li@intel.com>
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>