LU-4815 lfsck: pause LFSCK before server stack fini

LU-4815 lfsck: pause LFSCK before server stack fini

To avoid the LFSCK to access the devices/objects during
the targets stopping.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ifd8c1b1f878ac00a3c92ab6f2ab11e46003f584c
Reviewed-on: http://review.whamcloud.com/9774
Tested-by: Jenkins
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>