LU-2333 utils: mount.lustre to ignore fsname

LU-2333 utils: mount.lustre to ignore fsname

if MGS is the only service on a given device, then it's OK
to have empty fsname: fsname does not apply to MGS generally.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: Ie2269c46280b1ef2504fc73a61cc1d28ff2261fc
Reviewed-on: http://review.whamcloud.com/4592
Tested-by: Hudson
Reviewed-by: Prakash Surya <surya1@llnl.gov>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>