LU-4934 tests: Account for slow ZFS in sanity-lfsck/9a-b

LU-4934 tests: Account for slow ZFS in sanity-lfsck/9a-b

Allow lfsck speed to be too slow with ZFS due to it's performance
issues.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Id39d9468327a02b648ba2c8b4b131250946a04b1
Reviewed-on: http://review.whamcloud.com/10140
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>