Add missing symlink to roles

It turned out that the playbook
`playbooks/byo/openshift-preflight/check.yml` would only work under a
certain `ansible.cfg` in which `roles/` was added to `roles_path`.

It was the case with the example config prior to
b804e70cdd0bc8601bfc87fcf3e34043223828ee.

playbooks/byo/openshift-preflight/roles

@@ -0,0 +1 @@
+../../../roles