Fix docs build

It was broken by the updated docutils. The docutils version should be
fixed due to the openstack/requirements.

Partially Fixes: bug #1206670

Change-Id: Ie612519711cc8ebf9cb848f9d10826e74f2fa049
(cherry picked from commit 3de5642c6f7d77805d5892320637cf65ec2baf39)
Merge "Fix docs build" into stable/0.2