Adding third example for property protections

[Phillipa Avery]

In:
https://github.com/openstack/glance/blob/master/doc/source/property-protections.rst

Add third example: Limit all property interactions to admin only using policy rule context_is_admin defined in policy.json

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/53495
Committed: http://github.com/openstack/glance/commit/cdd39e0495b1d82f46ed1604966144e613f3f857
Submitter: Jenkins
Branch: master

commit cdd39e0495b1d82f46ed1604966144e613f3f857
Author: eos2102 <email address hidden>
Date: Wed Oct 23 21:08:22 2013 -0700

    Addition of third example for Property Protections

    Includes an example to limit all property interactions to admin only using policy rule
    context_is_admin defined in policy.json

    Change-Id: I22dddc06a84312b3b1cbd195cb84839e0321a9f0
    Closes-Bug: #1243945