Missing Info (Ocata): Install and configure controller node in Installation Guide

[Samuel Ghinet]

See https://docs.openstack.org/developer/nova/placement.html

Specifies:
"
Keep in mind that Placement is optional in Newton, but required in Ocata, so the placement service should be enabled before upgrading to Ocata. nova.conf on the compute nodes will need to be updated in the [placement] group for credentials to make requests from nova-compute to the placement-api service.
"

The current installation documentation / tutorial says nothing about the Placement API.

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [x] This doc is inaccurate in this way: Cannot function properly without configuring the Placement API
- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

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-----------------------------------
Release: 0.1 on 2017-03-17 08:37
SHA: 675046708243d34c303e8a89b3088df5556e0b21
Source: https://git.openstack.org/cgit/openstack/openstack-manuals/tree/doc/install-guide/source/nova-controller-install.rst
URL: https://docs.openstack.org/ocata/install-guide-rdo/nova-controller-install.html