Update glance-cache to support keystone service tenants

[Dan Prince]

Glance cache currently has a setting for admin_token in glance-cache.conf.

# Admin token to use if using Keystone
# admin_token = 123

This is used to create a context in order to talk to the Glance registry when queuing and prefetching images.

Now that we are using keystone service tenants... we should update Glance's cache to support them as well.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/5163

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/5163
Committed: http://github.com/openstack/glance/commit/4d41027d219429b44b1036c85b3fb4a09e530121
Submitter: Jenkins
Branch: master

commit 4d41027d219429b44b1036c85b3fb4a09e530121
Author: Dan Prince <email address hidden>
Date: Fri Mar 9 02:12:35 2012 -0500

    Glance cache updates to support Keystone Essex.

    Glance caching updates to support keystone service tenants:

     * Update glance-cache-manage so that it supports the same style OS_
      environment variables and CLI options for auth that bin/glance does.

     * Updates registry/client so that it supports Keystone KSL style
      service tenants. As services no longer use admin_tokens this is
      a requirement to be able to use caching w/ KSL.

    Fixes LP Bug #949486.

    Change-Id: I8d0e56a9ec0d20ef56ed2ce8b860d987ae159e01