ceph-iscsi: Improve 'tcmu-runner' section in ceph status output

Issue

• When we run the ceph -s command to see the cluster health and stats, it currently also lists every single iscsigw-pool-disks.
• If we have +50 iSCSI volumes, it becomes very difficult to see what is going on.

# ceph -s
  cluster:
    id:     554214df-ddf6-4f79-96a9-75770e8cbeda
    health: HEALTH_WARN
            too few PGs per OSD (4 < min 30)

  services:
    mon:         3 daemons, quorum ceph4node102,ceph4node100,ceph4node101 (age 4h)
    mgr:         ceph4node101(active, since 2h), standbys: ceph4node102, ceph4node100
    osd:         6 osds: 6 up (since 4h), 6 in (since 4h)

**tcmu-runner: 4 daemons active (ceph4admin4.example.com:rbd/disk_1, ceph4admin4.example.com:rbd/test, ceph4node100.example.com:rbd/disk_1, ceph4node100.example.com:rbd/test)**