Enable host aggregate metadata update doc

[OpenStack Infra]

https://review.openstack.org/110612
commit 473233c79633374eb78c5527c64f527eaf1a2c1c
Author: Michal Dulko <email address hidden>
Date: Thu Sep 11 19:30:17 2014 +0200

    Enable host aggregate metadata update

    Nova currently expose an api to let the users update
    the host aggregates metadata so horizon should expose
    this functionality. At the same time Glance is exposing
    a metadata dictionary in Juno, where users can register
    the key/value pairs that describe their cloud deployment.

    This patch uses the glance metadata api to expose the available
    metadata and the nova api to update the aggregates metadata

    Co-Authored-By: Santiago Baldassin <email address hidden>
    Co-Authored-By: Pawel Skowron <email address hidden>
    Co-Authored-By: Bartosz Fic <email address hidden>
    Co-Authored-By: Michal Dulko <email address hidden>
    Co-Authored-By: Pawel Koniszewski <email address hidden>
    DocImpact
    Change-Id: I4abf88426f548c47a21920169f710d3310e3ede6
    Implements: blueprint host-aggregate-update-metadata

[Anne Gentle (annegentle)]

Any doc patch for this would be in the End User Guide in the dashboard chapter, not in the API doc. That said, I don't think we have a documented use case where this would come up in a dashboard topic. Closing.