purge-docker-cluster: don't remove data on atomic

Because we don't manage the docker service on atomic (yet) via the
ceph-container-common role then we can't stop docker dans remove
the data.
For now let's do that only for non atomic hosts.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 638604929b)

infrastructure-playbooks/purge-docker-cluster.yml

@@ -714,8 +714,14 @@
       - /etc/ceph
       - /var/log/ceph
 
-  - name: remove data
-    shell: rm -rf /var/lib/ceph/* /var/lib/docker/*
+  - name: remove ceph data
+    shell: rm -rf /var/lib/ceph/*
+
+  # (todo): remove this when we are able to manage docker
+  # service on atomic host.
+  - name: remove docker data
+    shell: rm -rf /var/lib/docker/*
+    when: not is_atomic | bool
 
 - name: purge fetch directory