chore(ensure-nodejs-fork): downstream changes from ensure-nodejs

- Require node_version variable (the default has been removed).[1]
- Handle Node installations for all versions correctly.[2]

[1]: https://opendev.org/zuul/zuul-jobs/commit/e188ce71ca7361adfee668f8d17d0d78f360dc90
[2]: https://opendev.org/zuul/zuul-jobs/commit/efa55f881d6ee2681b008847372d69abf350ac21

Change-Id: Id1f5419aa49fc8ee631b2ba53389a4d982af7963
diff --git a/roles/ensure-nodejs-fork/README.rst b/roles/ensure-nodejs-fork/README.rst
index 09f7e06..eda1905 100644
--- a/roles/ensure-nodejs-fork/README.rst
+++ b/roles/ensure-nodejs-fork/README.rst
@@ -3,4 +3,5 @@
 **Role Variables**
 
 .. zuul:rolevar:: node_version
-   :default: 6
+
+   Required. What version of Node to install.