LU-5122 lfsck: maintain the MDT devices list properly

LU-5122 lfsck: maintain the MDT devices list properly

The layout LFSCK needs to know which MDT/OST devices have taken part
in the LFSCK, it maintains two lists for that. When the layout LFSCK
starts/stops, it should handle the two lists separately and properly.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I26103ddc7796dbb1706f5c4da3737df297214e68
Reviewed-on: http://review.whamcloud.com/10507
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>