nova-specs docs builds fail with sphinx 1.6.1: Citation is not referenced.

[Matt Riedemann]

I noticed this today:

http://logs.openstack.org/81/461481/3/gate/gate-nova-specs-docs-ubuntu-xenial/9e65575/console.html#_2017-05-23_18_19_21_056047

2017-05-23 18:19:21.056047 | /home/jenkins/workspace/gate-nova-specs-docs-ubuntu-xenial/doc/source/specs/juno/implemented/pci-passthrough-sriov.rst:413:Citation [BIND_PRF] is not referenced.

And reproduced it locally. It looks like the problem is in Sphinx 1.6.1. Blocking that version and using 1.5.6, which is what is in upper-constraints:

https://github.com/openstack/requirements/blob/master/upper-constraints.txt#L341

Fixes it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/467367

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/467367
Committed: https://git.openstack.org/cgit/openstack/nova-specs/commit/?id=820f5a91cc4769877e8e8c494db63111dee541ba
Submitter: Jenkins
Branch: master

commit 820f5a91cc4769877e8e8c494db63111dee541ba
Author: Matt Riedemann <email address hidden>
Date: Tue May 23 15:34:17 2017 -0400

    Blacklist sphinx 1.6.1

    For some reason this release makes docs builds fail because it
    can't resolve citations. The version in upper-constraints, which
    we don't use in this repo, is 1.5.6, so blacklisting 1.6.1 seems
    fine.

    Change-Id: I2b73370876c80a88bd4a48db7fdd6ac23ace4503
    Closes-Bug: #1693010