(Import Refactor) Make tasks API admin only

[Flavio Percoco]

This is a sub-task for the image import process work: https://review.openstack.org/#/c/232371/

One of the goals of this spec is to improve the image import process and allow for other background operations to be executed when the image data is added. This supersedes the need of the task endpoint that we'll slowly deprecate. As part of this spec, we should make it admin only and warn deployers that this API is going to be deprecated.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/265448

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/265448
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=8f0d6ea9c535f6ab09fc9b2ae84cf0bef2401ee4
Submitter: Jenkins
Branch: master

commit 8f0d6ea9c535f6ab09fc9b2ae84cf0bef2401ee4
Author: Flavio Percoco <email address hidden>
Date: Fri Jan 8 16:38:49 2016 -0430

    Make the task's API admin only by default

    One of the goals of this spec is to improve the image import process and
    allow for other background operations to be executed when the image data
    is added. This supersedes the need of the task endpoint that we'll
    slowly deprecate. As part of this spec, we should make it admin only and
    warn deployers that this API is going to be deprecated.

    MitakaPriority
    DocImpact: Tasks API is now admin only. Deployments depending on this
        API need to make sure they make it accessible for non-admins.
    Closes-bug: #1527716
    Partially-blueprint: image-import-refactor
    Change-Id: I28cb69ea730ae58b9aed1dd43b68305dbbf132c1