Fix publish-openstack-docs-pti check/gate html

The new publish-openstack-docs-pti template uses the openstack-tox-docs
job which does not save the rendered docs, nor does it set the job link
to the rendered documents.
This patch changes the openstack-tox-docs job to save the rendered html
and set the success-url to the rendered html documents.
This returns the behavior the publish-openstack-sphinx-docs job provided.

Change-Id: I460c00542426f6b24a7423098be9a0af14a35f01

playbooks/docs/post.yaml

@@ -0,0 +1,3 @@
+- hosts: all
+  roles:
+    - fetch-sphinx-output

zuul.d/jobs.yaml

@@ -556,6 +556,10 @@
       Uses tox with the ``docs`` environment.
     vars:
       tox_envlist: docs
+    success-url: html/
+    roles:
+      - zuul: openstack-infra/zuul-jobs
+    post-run: playbooks/docs/post.yaml
 
 - job:
     name: openstack-tox-with-oslo-master-base