metadefs release note for pike

[Brian Rosmaita]

Instead of requiring separate release notes for each metadefs change, we'll gather them into a single yaml file in releasenotes/notes.

Start with a releasenote for Change-Id: I825c5c2a8ba3b9f5eccd9800870b6307d201614c

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/476522

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/476522
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=ccf07eeec56a8d40da5b94ba8227f0887086e2f0
Submitter: Jenkins
Branch: master

commit ccf07eeec56a8d40da5b94ba8227f0887086e2f0
Author: Brian Rosmaita <email address hidden>
Date: Thu Jun 22 09:34:30 2017 -0400

    Add metadefs release note for Pike

    Metadefs changes for Pike will be described in a single release note.
    This patch introduces the file and the first change. Other metadefs
    changes in Pike should include a change to this file.

    Change-Id: Id71acaf54e2fa623e1af247d5ddcafc27f55ee75
    Partial-bug: #1699549

[Brian Rosmaita (brian-rosmaita)]

This made it into RC-1, I forgot to put closes-bug on the patch.
Change-Id: I466463e1f921d1d07227b987b7d80274fcdd5f42