LU-7661 mgs: restrict MGS_SET_INFO to stripe parameters

LU-7661 mgs: restrict MGS_SET_INFO to stripe parameters

The MGS_SET_INFO RPC is only needed for setting the default striping
on a filesystem, so in mgs_set_info() reject attempts to set a
parameter that is not of the form *.lov.stripe{count,size,offset}=*.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I5ac693f886fd035ab639e03628849e791e1e2e9a
Reviewed-on: http://review.whamcloud.com/17982
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Jeremy Filizetti <jeremy.filizetti@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>