Devstack local.conf requires updating.

- [x] This doc is inaccurate in this way:

Currently the devstack local.conf section contains the following

CINDER_BRANCH=stable/OPENSTACK_VERSION
CEILOMETER_BRANCH=stable/OPENSTACK_VERSION
GLANCE_BRANCH=stable/OPENSTACK_VERSION
HEAT_BRANCH=stable/OPENSTACK_VERSION
HORIZON_BRANCH=stable/OPENSTACK_VERSION
KEYSTONE_BRANCH=stable/OPENSTACK_VERSION
NEUTRON_BRANCH=stable/OPENSTACK_VERSION
NOVA_BRANCH=stable/OPENSTACK_VERSION
SWIFT_BRANCH=stable/OPENSTACK_VERSION
ZAQAR_BRANCH=stable/OPENSTACK_VERSION

This allows you to set the stable version you want DEVSTACK to install. I believe that we should also include

REQUIREMENTS_BRANCH=stable/OPENSTACK_VERSION

This will ensure we pull the correct requirements files as well. Saving frustration when latest has moved forward, and old stable versions require older versions of packages.

-----------------------------------
Release: 0.9.19.dev7 on None
SHA: aae4528eeb706a9868b0ea588b325da3fcd69853
Source: http://git.openstack.org/cgit/openstack/python-openstacksdk/tree/doc/source/contributors/testing.rst
URL: https://developer.openstack.org/sdks/python/openstacksdk/contributors/testing.html