LU-5778 lod: Fix lod_qos_statfs_update()

LU-5778 lod: Fix lod_qos_statfs_update()

When an OST is sick, or unactivate, lod cannot fetch its statfs
information. In lod_qos_statfs_update() this was preventing lod
to get information for other OST because refresh was stopped at
first error.
This patch fixes this behaviour.

Signed-off-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Change-Id: Id0217f228381ef7a41fdbfd99f5499dcc97ace0e
Reviewed-on: http://review.whamcloud.com/12617
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>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>