purge-docker-cluster: default raw_journal_devices to []

If we're purging a containerized cluster that did not use the
raw_multi_journal OSD scenario then raw_journal_devices will not be
defined which causes the playbook to fail.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1455187

Signed-off-by: Andrew Schoen <aschoen@redhat.com>

infrastructure-playbooks/purge-docker-cluster.yml

@@ -249,7 +249,7 @@
       zap_device
     with_items:
       - "{{ ceph_osd_docker_devices }}"
-      - "{{ raw_journal_devices }}"
+      - "{{ raw_journal_devices|default([]) }}"
 
   - name: wait until the zap containers die
     shell: |
@@ -267,7 +267,7 @@
       state: absent
     with_items:
       - "{{ ceph_osd_docker_devices }}"
-      - "{{ raw_journal_devices }}"
+      - "{{ raw_journal_devices|default([]) }}"
 
   - name: remove ceph osd service
     file: