Functional testing: add journal-to-console element

This element redirects the systemd journal to the console.  It can be
helpful if the inner VM isn't booting; when it times out nodepool will
dump the console into the logs.  With this enabled, you'll be able to
see various useful output such as NetworkManager getting addresses,
etc.

Depends-On: https://review.opendev.org/669784
Change-Id: I608b8cd9e467351c996fc5f51f15ee67f4570ba3

playbooks/nodepool-functional-openstack/templates/nodepool.yaml.j2

@@ -52,6 +52,7 @@ diskimages:
       - devuser
       - openssh-server
       - nodepool-setup
+      - journal-to-console
     release: '{{ nodepool_diskimage.release }}'
     env-vars:
       TMPDIR: '{{ NODEPOOL_DIB_BASE_PATH }}/tmp'