LU-2155 utils: Enable ldiskfs mmp on tunefs failover add

LU-2155 utils: Enable ldiskfs mmp on tunefs failover add

Enable Multi-Mount Protection in ldiskfs when adding a failover peer
via tunefs.  MMP is enabled in mkfs if failover is configured
initially, but it wasn't if failover was added later.

Signed-off-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Change-Id: Ie21ef5324de240afe0fd760cb4a9b3e1b4165064
Reviewed-on: https://review.whamcloud.com/26758
Tested-by: Jenkins
Reviewed-by: Zhiqi Tao <zhiqi.tao@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>