Document Compute extension os-multiple-create

[Anne Gentle]

Went in with review:

https://review.openstack.org/#/c/11090/

Key min_count, max_count, ret_res_id off of ext.

Implements part of blueprint disable-server-extensions

Adds a new extension descriptor callsed os-multiple-create. Modifies
the min_count, max_count, and return_reservation_id parameters to
server create to only be allowed if the extension is enabled.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/19303

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/19303
Committed: http://github.com/openstack/api-site/commit/4f4664d0ab323a36cc62be155f4d1c6f813d6f15
Submitter: Jenkins
Branch: master

commit 4f4664d0ab323a36cc62be155f4d1c6f813d6f15
Author: annegentle <email address hidden>
Date: Wed Jan 9 10:53:18 2013 -0600

    Adds os-multi-create extension docs in separate section.

    Fix bug 1039769

    Patchset adds the WADL file I meant to git add.

    Change-Id: Ib909cda827be885a65d1d78304dbc359906ad93c