Updated openstack/openstack
Project: openstack/oslo.db  87fc4d39de66b5d9f215431b66ff55820efcb1d8

Added ``docs`` environment to tox.ini

Added the new tox environment to build docs.
Fixes in oslo.db documentation building

Change-Id: Icab4f299df3d8a4c40dc4fd7292609109f206afd