LU-2887 tests: disable SLOW for ZFS in parallel-scale

LU-2887 tests: disable SLOW for ZFS in parallel-scale

Because all zfs pools are on the same physical device in autotest
ZFS backed OSTs run VERY slowly so disable SLOW.  Decrease load on zfs
backed MDS.

Test-Parameters: envdefinitions=SLOW=yes,ENABLE_QUOTA=yes mdtfilesystemtype=zfs mdsfilesystemtype=zfs ostfilesystemtype=zfs testlist=parallel-scale
Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: I99d980adcf4259f8431c351ce6fecb1088419130
Reviewed-on: http://review.whamcloud.com/7778
Tested-by: Jenkins
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>