Add appendix to remove juju elements from infra machine

docs/infra_nodes.md

@@ -23,3 +23,17 @@ Once the machines have been added, we can deploy the infra model
 cd config
 ./juju_deploy_infra.sh
 ```
+
+# Appendix A
+
+In a scenario, that the controllers and the cloud is being re-provisioned, but these
+physical machines are still here and a `juju kill-controller` may have run, then we
+need to do some cleanup to be able to re-run the commands above to add the infra
+model.
+
+```bash
+for i in asrock01 asrock02 asrock03
+do
+    ssh $i -- sudo rm -rf /var/log/juju/ /var/lib/juju/ /etc/systemd/system/jujud-*
+done
+```