osd_disk_activate: fix osd umount on container stop

There's no need to have complexity to get the path of the current OSD.

By the way, at the moment this complexity leads to incorrect behavior:

```
-bash-4.2# docker exec ceph-osd-2 findmnt --nofsroot --noheadings --output SOURCE --submounts --target /var/lib/ceph/osd/
/dev/mapper/atomicos-root
/dev/sdb1
/dev/sda1
-bash-4.2# docker exec ceph-osd-2 df --output=target | grep '/var/lib/ceph/osd/'
/var/lib/ceph/osd/ceph-0
/var/lib/ceph/osd/ceph-2
-bash-4.2#
```

In the first method used in recent branches, it means we might try to umount
the root partition.
In the second method used in older branches we try to umount something
messed up:
```
2021-01-14 00:17:08  /opt/ceph-container/bin/entrypoint.sh: osd_disk_activate: Unmounting /var/lib/ceph/osd/ceph-0
/var/lib/ceph/osd/ceph-2

...

umount: /var/lib/ceph/osd/ceph-0
/var/lib/ceph/osd/ceph-2: mountpoint not found
++/opt/ceph-container/bin/osd_disk_activate.sh:92: sigterm_cleanup_post(): log 'osd_disk_activate: Failed to umount /var/lib/ceph/osd/ceph-0
/var/lib/ceph/osd/ceph-2'

...

++/opt/ceph-container/bin/common_functions.sh:13: log(): echo '2021-01-14 00:17:08  /opt/ceph-container/bin/entrypoint.sh: osd_disk_activate: Failed to umount /var/lib/ceph/osd/ceph-0
/var/lib/ceph/osd/ceph-2'

```
We can easily build and predict the path to umount since we have
`$CLUSTER` and `$OSD_ID` variables in the code of `osd_disk_activate.sh`

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1921750

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit bd6fe34)

src/daemon/osd_scenarios/osd_disk_activate.sh

@@ -80,14 +80,18 @@ function osd_activate {
   fi
   apply_ceph_ownership_to_disks
 
+  if [[ ${OSD_DMCRYPT} -eq 1 ]]; then
+    umount_lockbox
+  fi
+
   log "SUCCESS"
   # This ensures all resources have been unmounted after the OSD has exited
   # We define `sigterm_cleanup_post` here because:
   # - we want to 'protect' the following `exec` in particular.
   # - having the cleaning code just next to the concerned function in the same file is nice.
   function sigterm_cleanup_post {
     local osd_mnt
-    osd_mnt=$(df --output=target | grep '/var/lib/ceph/osd/')
+    osd_mnt="/var/lib/ceph/osd/${CLUSTER}-${OSD_ID}"
     log "osd_disk_activate: Unmounting $osd_mnt"
     umount "$osd_mnt" || (log "osd_disk_activate: Failed to umount $osd_mnt"; lsof "$osd_mnt")
   }

src/daemon/osd_scenarios/osd_volume_activate.sh

@@ -102,11 +102,9 @@ function osd_volume_activate {
   # - having the cleaning code just next to the concerned function in the same file is nice.
   function sigterm_cleanup_post {
     local ceph_mnt
-    ceph_mnt=$(findmnt --nofsroot --noheadings --output SOURCE --submounts --target /var/lib/ceph/osd/"${CLUSTER}-${OSD_ID}" | grep '^/')
-    for mnt in $ceph_mnt; do
-      log "osd_volume_activate: Unmounting $mnt"
-      umount "$mnt" || (log "osd_volume_activate: Failed to umount $mnt"; lsof "$mnt")
-    done
+    ceph_mnt="/var/lib/ceph/osd/${CLUSTER}-${OSD_ID}"
+    log "osd_volume_activate: Unmounting $ceph_mnt"
+    umount "$ceph_mnt" || (log "osd_volume_activate: Failed to umount $ceph_mnt"; lsof "$ceph_mnt")
 
     UUIDS=$(get_dmcrypt_uuids)