'docker_image' above but some containers share a common set of
config files which are generated in a common base container.
+ * docker_puppet_tasks: This section provides data to drive the
+ docker-puppet.py tool directly. The task is executed only once
+ within the cluster (not on each node) and is useful for several
+ puppet snippets we require for initialization of things like
+ keystone endpoints, database users, etc. See docker-puppet.py
+ for formatting.
+
Docker steps
------------
Similar to baremetal docker containers are brought up in a stepwise manner.