LU-7223 test: check mmp feature properly in mmp.sh

The mmp.sh checks if the mmp feature is enabled by looking at
the failover_HOST variables, which is not reliable, this patch
changed it to looking at the features on device directly.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: Ia86d1bfbfa56e01efa06955a36fa34ca62997a54
Reviewed-on: http://review.whamcloud.com/17884
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>