LU-13460 lfs: use correct obd index in print_failed_tgt()

LU-13460 lfs: use correct obd index in print_failed_tgt()

In function print_failed_tgt(), when calling llapi_obd_statfs(),
the correct obd index should be used according to obd type.

sanity.sh test_56rb is added to verify this patch.

Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I443a5b388ee1c3efc8fc589c09aeec6f9b71600b
Reviewed-on: https://review.whamcloud.com/38264
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>