Deprecate `show_multiple_locations` option

[OpenStack Infra]

https://review.openstack.org/313936
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.
Your project "openstack/glance" is set up so that we directly report the documentation bugs against it. If this needs changing, the docimpact-group option needs to be added for the project. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit dbfc121072dff4981532b068bb210f9c73c7b98c
Author: Flavio Percoco <email address hidden>
Date: Sun May 8 11:06:33 2016 -0400

    Deprecate `show_multiple_locations` option

    There are currently several ways to disable/enable multiple_locations.
    One is through a global config option (show_multiple_locations) and the
    other one is through a more granular RBAC using Glance's policies.

    Maintaining two different ways to configure, enable and/or disable a
    feature is painful for developers and operators. Given that we have a
    more granular way to manage this feature and that it's the preferred one
    given the provided ability to chose what each role can/cannot do, this
    patch proposes to remove the global config option.

    There have been concerns about this proposal mostly on the fact that
    it'll remove the ability to "turn off" the entire feature with a single
    option. This doesn't seem to be a strong enough motivation to warrant
    the effort of maintaining these 2 options.

    This patch marks the aforementioned option as deprecated.

    UpgradeImpact
    DocImpact

    Co-Authored-By: Flavio Percoco <email address hidden>
    Co-Authored-By: Nikhil Komawar <email address hidden>

    Lite-spec: https://review.openstack.org/360220
    Change-Id: I1c5cb7834c2cf3295e10bad7fd07cfacb8e4ac50

[Brian Rosmaita (brian-rosmaita)]

Done:
* This is documented in the sample config file as part of the help-text-improvements initiative.
* It's also documented in the release notes for Newton.

Check:
* It should be included in the operations manual by the inclusion of the sample config file.
* Do a quick scan of the Glance dev docs and see if it's mentioned anywhere

[Brian Rosmaita (brian-rosmaita)]

Not mentioned anywhere in the dev docs.

Deprecation is noted in the OpenStack Configuration Reference.

[Brian Rosmaita (brian-rosmaita)]

To summarize, the doc impact of this bug was already dealt with in the Newton release.