LU-6442 utils: "-G <value>" can be passed through mkfs options

LU-6442 utils: "-G <value>" can be passed through mkfs options

mkfs.lustre util checks if parametrs already contain "flex_bg"
option (number of block groups that will be packed together
to create a larger virtual block group)  and adds this option
if it doesn't exists. But second parameter "-G" (number of block
groups that will be packed together to create a larger virtual
block group) can be added twice: one passed through mkfs options
and another one - default value. In this case this parameter
is not changed actually and default value is applied.

This patch adds extra check. Default option "-G" is added
only if no "-G" option passed through mkfs options.

Xyratex-bug-id: MRP-2046
Signed-off-by: Artem Blagodarenko <artem_blagodarenko@xyratex.com>
Reviewed-by: Sergey Cheremencev <sergey_cheremencev@xyratex.com>
Tested-by: Elena Gryaznova <elena.gryaznova@seagate.com>
Reviewed-by: Vitaly Fertman <vitaly.fertman@seagate.com>
Change-Id: I14fb5f8d10fa369428efcbbcb4f638f388979818
Reviewed-on: http://review.whamcloud.com/14400
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>