switch_to_containers: umount osd lockbox partition

switch_to_containers: umount osd lockbox partition

When switching from a baremetal deployment to a containerized deployment
we only umount the OSD data partition.
If the OSD is encrypted (dmcrypt: true) then there's an additional
partition (part number 5) used for the lockbox and mount in the
/var/lib/ceph/osd-lockbox/ directory.
Because this partition isn't umount then the containerized OSD aren't
able to start. The partition is still mount by the system and can't be
remount from the container.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1616159
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 19edf707a50c2e86110b2ba0231091b6bd355bd1)