Docs needed for optional placement database

[Matt Riedemann]

Blueprint https://blueprints.launchpad.net/nova/+spec/optional-placement-database added support for configuring a separate database for the placement service so it's not just part of the nova_api database (even though it's the same schema for now).

This is important for extracting placement from nova, and should be part of a new base install so people don't have to migrate later.

There are at least two places we should update in the docs:

1. The install guide for fresh installs should tell people to create a database for placement and configure nova.conf appropriately using the new placement database config options.

Looking at the install guide, we have 3 different guides to update (ubuntu, rdo, suse), but looks like:

a) https://docs.openstack.org/nova/latest/install/controller-install-ubuntu.html#prerequisites - create a placement database using the nova_api schema.

b) configure the placement db

https://docs.openstack.org/nova/latest/install/controller-install-ubuntu.html#install-and-configure-components

I think that's it. "nova-manage api_db sync" will sync the placement database and the nova_api database, so we should be good there.

2. Update the placement upgrade docs for Rocky to mention the new config option and, at a high level, the options people have for migrating from nova_api to placement db, e.g. stop api services, copy the nova_api db, deploy placement db using the nova_api copy, config and restart api services.

https://docs.openstack.org/nova/latest/user/placement.html#rocky-18-0-0

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/578013

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/581151
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=cc7f4ea7248a692237ede41531f523050a8550f2
Submitter: Zuul
Branch: master

commit cc7f4ea7248a692237ede41531f523050a8550f2
Author: Chris Dent <email address hidden>
Date: Mon Jul 9 23:29:28 2018 +0100

    Update some placement docs to reflect modern times

    This change provides a small number of updates to the placement user and
    contributor documentation to reflect some of the things that have
    changed recently. This is by no means complete, but is an improvement
    over what was there.

    Partial-Bug: #1778227

    Change-Id: Ia348cd3c99b1a5104e15595fdebc83e1ca582a98

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/578013
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=e06c287cbf0639d85533b27527ffd562898db9af
Submitter: Zuul
Branch: master

commit e06c287cbf0639d85533b27527ffd562898db9af
Author: chenxing <email address hidden>
Date: Tue Jun 26 03:38:08 2018 -0400

    Update install guide for placement database configuration

    Change-Id: I295fe539321bcce3449b522d54121985577c4b35
    Partial-Bug: #1778227

[Chris Dent (cdent)]

This is differently out of date now that we have an extracted placement.