tox docs fails with ../contributor/api/modules.rst:document isn't included in any toctree

[Trinh Nguyen]

I fails the docs test with this error:

2018-05-31 07:43:48.428126 | ubuntu-xenial | looking for now-outdated files... none found
2018-05-31 07:43:48.581841 | ubuntu-xenial | pickling environment... done
2018-05-31 07:43:48.582609 | ubuntu-xenial | checking consistency...
2018-05-31 07:43:48.582673 | ubuntu-xenial | Warning, treated as error:
2018-05-31 07:43:48.582782 | ubuntu-xenial | /home/zuul/src/git.openstack.org/openstack/tacker/doc/source/contributor/api/modules.rst:document isn't included in any toctree

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/572305

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/570831
Committed: https://git.openstack.org/cgit/openstack/tacker/commit/?id=6fa307b85e92bcacc49edd15e82859a6aa720613
Submitter: Zuul
Branch: master

commit 6fa307b85e92bcacc49edd15e82859a6aa720613
Author: Trinh Nguyen <email address hidden>
Date: Tue May 29 11:34:13 2018 +0900

    Add Dynamic VNFFG usage guide

    This patch also reorders the user guide index page.
    And fix a docs test with tox.

    Change-Id: I0522f6aa40d47f40178820a99a2723ba2af9cf72
    Closes-Bug: #1774356

[OpenStack Infra (hudson-openstack)]

Change abandoned by Trinh Nguyen (<email address hidden>) on branch: master
Review: https://review.openstack.org/572305