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.

Patch backported from master:
Lustre-change: http://review.whamcloud.com/12617
Lustre-commit: b50a6ccf9fe32c2fae1e6225f8e1a5b420b45d56

Signed-off-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Change-Id: I26ea91e54275f9e1accf51b779edf1b6e6a796a0
Reviewed-on: http://review.whamcloud.com/12685
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>