Add a policy to control setting 'location' parameter

[Stuart McLaren]

It might be useful to have a policy to control whether the 'location' field can be set or not, eg:

$ cat /etc/glance/policy.json
{
    "default": "",
    "manage_image_cache": "role:admin",
    "publicize_image": "role:admin",
    "set_image_location": "role:admin" <<<
}

this would allow an operator to enable/disable the x-image-meta-location functionality for regular users, and if desired, prevent 'external' image data being referenced.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/24095

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/24095
Committed: http://github.com/openstack/glance/commit/f17f4837e06f90d2132bcdf651eaf37ea2dba180
Submitter: Jenkins
Branch: master

commit f17f4837e06f90d2132bcdf651eaf37ea2dba180
Author: Stuart McLaren <email address hidden>
Date: Mon Mar 11 17:59:32 2013 +0000

    Add 'set_image_location' policy option

    Gives operators the option to prevent references to 'external' image data.

    Addresses bug 1153613.

    Change-Id: I68aac9039eed0f70ed3b893f5c51838a70d290ae