Add conditional for versioned url (#6712)

Checks an additional variable named versionedurl for the version name,
and uses the value as the url to reference. If the versionedurl doesn't
contain an entry for the version the current path is used.

e.g.

versionedurl:
  v1.8: /docs/home
  v1.7: /docs/old-path-to-doc

_config.yml

@@ -27,27 +27,27 @@ defaults:
           version: "v1.9"
           githubbranch: "v1.9.0"
           docsbranch: "release-1.9"
-          url: https://kubernetes.io/docs/home/
+          url: https://kubernetes.io
         - fullversion: "v1.8.4"
           version: "v1.8"
           githubbranch: "v1.8.4"
           docsbranch: "release-1.8"
-          url: https://v1-8.docs.kubernetes.io/docs/home/
+          url: https://v1-8.docs.kubernetes.io
         - fullversion: "v1.7.6"
           version: "v1.7"
           githubbranch: "v1.7.6"
           docsbranch: "release-1.7"
-          url: https://v1-7.docs.kubernetes.io/docs/home/
+          url: https://v1-7.docs.kubernetes.io
         - fullversion: "v1.6.8"
           version: "v1.6"
           githubbranch: "v1.6.8"
           docsbranch: "release-1.6"
-          url: https://v1-6.docs.kubernetes.io/docs/home/
+          url: https://v1-6.docs.kubernetes.io
         - fullversion: "v1.5.7"
           version: "v1.5"
           githubbranch: "v1.5.7"
           docsbranch: "release-1.5"
-          url: https://v1-5.docs.kubernetes.io/docs/
+          url: https://v1-5.docs.kubernetes.io
       deprecated: false
       currentUrl: https://kubernetes.io/docs/home/
       nextUrl: http://kubernetes-io-vnext-staging.netlify.com/

_includes/header.html

@@ -16,7 +16,11 @@
                 </a>
                 <ul>
                 {% for version in page.versions %}
-                  <li><a href="{{ version.url }}">{{ version.version }}</a></li>
+                    {% if page.versionedurl contains version.version %}
+                    <li><a href="{{ version.url }}{{ page.versionedurl[version.version] }}">{{ version.version }}</a></li>
+                    {% else  %}
+                    <li><a href="{{ version.url }}{{ page.url }}">{{ version.version }}</a></li>
+                    {% endif %}
                 {% endfor %}
                 </ul>
               </li>