LU-13440 obdclass: server qos penalty miscaculated

LU-13440 obdclass: server qos penalty miscaculated

Server qos penalty calculation uses active target count, but it
should use server count, which will make it larger than expected,
then weight of targets are often 0, and finally cause MDT0 is
often chosen in qos allocation.

Lustre-change: https://review.whamcloud.com/43385
Lustre-commit: 0ccce7ecb72f847f4235a513424d90119edad7ca

Fixes: 45222b2ef ("LU-12624 obdclass: lu_tgt_descs cleanup")
Signed-off-by: Lai Siyao <lai.siyao@whamcloud.com>
Change-Id: I1982363e4ff74c7344dd5e07d04e29214afa8a7f
Reviewed-on: https://review.whamcloud.com/43399
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>