Document how an undercloud can be cleaned-up

This procedure has been tested on Train and onward and aims to be for
devs, although it's enough for any undercloud to be cleaned-up and
re-installed later.

Change-Id: I7dc7f2903f9a624cf8b4032606652113245b88a8

deploy-guide/source/deployment/install_undercloud.rst

@@ -255,3 +255,40 @@ used for undercloud deployment are stored in the tempdir
     with a permission error, log out and log in again. The stack user does get added
     to the docker group during install, but that change gets reflected only after a
     new login.
+
+Cleaning the Undercloud
+-----------------------
+
+This procedure isn't cleaning everything that TripleO generates, but enough
+so an Undercloud could be re-deployed.
+
+.. note::
+    This procedure has been tested on Train and onward. There is no guarantee
+    that it works before this version, due to container commands and
+    new directories.
+
+#. Log in to your machine (baremetal or VM) where you want to cleanup the
+   undercloud as a non-root user (such as the stack user)::
+
+       ssh <non-root-user>@<undercloud-machine>
+
+#. Cleanup the containers and their images::
+
+       sudo podman rm -af
+       sudo podman rmi -af
+
+#. Remove directories generated by TripleO::
+
+       sudo rm -rf \
+           /var/lib/tripleo-config \
+           /var/lib/config-data \
+           /var/lib/container-config-scripts \
+           /var/lib/container-puppet \
+           /var/lib/heat-config \
+           /var/lib/image-service \
+           /var/lib/mysql
+
+#. Cleanup systemd::
+
+       sudo rm -rf /etc/systemd/system/tripleo*
+       sudo systemctl daemon-reload