Add validate-host to base-minimal

The intent of leaving validate-host out of base minimal was to
run integration tests on it.
However, validate-host currently contains tasks that can't be
tested outside of a trusted context due to tasks that require
running on the executor.

validate-host is the role that creates the zuul-info directory
with the job inventory and variables, making it valuable to
troubleshoot integration jobs. Let's add it.

Change-Id: Ifad37daf1db116e29cbf18b242dff2959bce0331

playbooks/base-minimal/pre.yaml

@@ -2,3 +2,7 @@
   roles:
     - add-build-sshkey
     - start-zuul-console
+    - role: validate-host
+      # TODO(mordred) When we have site-local variables, these should go there
+      zuul_traceroute_host: git.openstack.org
+      zuul_image_manifest: /etc/dib-builddate.txt