LU-3856 mount: fix volume label update

LU-3856 mount: fix volume label update

The -n|--nomtab options is used to do not update
/etc/mtab after mount, but this option prevents to
update volume label also. This patch resolve this issue.

Signed-off-by: Alexander Boyko <alexander_boyko@xyratex.com>
Xyratex-bug-id: MRP-1325
Change-Id: Ib39de6a64c0aaeb4eff1b8d88fd7c9d4514c6c7e
Reviewed-on: http://review.whamcloud.com/7712
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Hudson
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>