purge: do not fail on purge ceph files

purge: do not fail on purge ceph files

On systems running docker there is an issue with lxfs that results in
the find command returning 1 but actually did the job.
e.g: on a system with docker runnning find /var will give us the
following error:

find:
'/var/lib/lxcfs/cgroup/devices/lxc/x1/system.slice/systemd-update-utmp.service/devices.deny':
Permission denied
find:
'/var/lib/lxcfs/cgroup/devices/lxc/x1/system.slice/dev-random.mount/devices.allow':
Permission denied
...
...

However ceph files got deleted so we ignore the error.

Signed-off-by: Sébastien Han <seb@redhat.com>