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 trough 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.