LU-6978 utils: mkfs.lustre to recognise non ldiskfs opts

LU-6978 utils: mkfs.lustre to recognise non ldiskfs opts

After "LU-6030 osd-ldiskfs: improve mount option handling landing",
mkfs.lustre lost ability to store non ldiskfs persistent options, because their
support was stripped out from ldiskfs layer.
This patch makes ldiskfs mount independent from the mount options from mkfs.lustre
command string.

Change-Id: I63e2efb84249eae8294ce33a72894aeb52563ad5
Xyratex-bug-id: MRP-2819
Signed-off-by: Alexander Zarochentsev <alexander.zarochentsev@seagate.com>
Reviewed-on: http://review.whamcloud.com/15937
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>