purge-docker-cluster: ensure old logs are removed

purge-docker-cluster: ensure old logs are removed

purge-docker-cluster must remove all osd_disk_prepare logs in
`{{ ceph_osd_docker_run_script_path }}`, otherwise if you purge your
cluster and try to redeploy it, osds will fail to start since because it
will try to retrieve find a partition uuid which doesn't exist.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1510470
Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>