LU-1267 lfsck: framework (2) for MDT-OST consistency

The LFSCK can talk with OSP directly, then the LFSCK on the MDT can
control/monitor the specified LFSCK instance on other targets (MDTs
or/and OSTs) without breaking dt_device APIs nor making OSP to know
the LFSCK things, and simplify the handling of remote OST-object or
MDT-object. For that, each OSP will register to the LFSCK will they
are added into the system. The LFSCK maintains such target table in
RAM with the similar logic as the LOD does.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ifa14db68925a0cd2afe0c3566382dbb6176d50b2
Reviewed-on: http://review.whamcloud.com/8302
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>