LU-6626 utils: lfs_getstripe prints empty pool name

LU-6626 utils: lfs_getstripe prints empty pool name

When the stripe version is V3, yet pool name is empty, the
lfs getstripe command will prints an empty pool name. That is
confusing since the user might think there is a pool for this
directory.

Signed-off-by: Li Xi <lixi@ddn.com>
Change-Id: I4338362331bc958686464bfdfea647c90244f818
Reviewed-on: http://review.whamcloud.com/14906
Tested-by: Jenkins
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>