purge: use sysfs to unmap rbd devices

purge: use sysfs to unmap rbd devices

in containerized context, using the binary provided in atomic os won't
work because it's an old version provided by ceph-common based on
10.2.5.
Using a container could be an idea but for large cluster with hundreds
of client nodes, that would require to pull the image of each of them
just to unmap the rbd devices.

Let's use the sysfs method in order to avoid any issue related to ceph
version that is shipped on the host.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1766064
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit 3cfcc7a105156dfde65b23e9d8662cd848537094)