Implement V3 Specific Version of EC2 Contrib

[OpenStack Infra]

https://review.openstack.org/70631
commit 9d5f33af07119b81a2038b3c95aab7c592cad1f5
Author: Morgan Fainberg <email address hidden>
Date: Sun Feb 2 14:02:20 2014 -0800

    Implement V3 Specific Version of EC2 Contrib

    Implement an EC2 Controller that returns a V3 token when invoked
    via the V3 pipeline. Moved all code except the `authenticate` method
    into a common base class mixin. `authenticate()` has become an
    abstract method. Shared code from `authenticate()` was moved into
    `_authenticate()`.

    V3 specific router definition added that makes use of the new V3
    specific controller.

    For upgrade purposes:
    * The paste.ini for keystone will need to be modified to include
      the new V3 ec2credentials in the pipeline as is documented in
      the updated sample paste.ini.
    * Policy.json updated to provide rules for the new V3 EC2credential
      CRUD as show in the updated sample policy.json and
      policy.v3cloudsample.json

    For authentication that occurs via the V3 ec2credential system,
    the response auth_method (encoded in the token) will be
    "ec2credential". This should have no impact on using
    or consuming the token itself but can be used to identify if
    the token was issued via the Ec2ControllerV3.authenticate
    method.

    The V2 version of ec2credential controller has been marked
    as deprecated to keep in line with the rest of the V2 API
    being deprecated (slated for removal in K).

    DocImpact
    UpgradeImpact

    Change-Id: Iaf1e05a1beef481385c6eb19d7f54cdc84b5b5df
    Closes-Bug: #1269947
    bp: deprecated-as-of-icehouse

[Tom Fifield (fifieldt)]

Addressed by adding to the upgrade notes for keystone: https://wiki.openstack.org/wiki/ReleaseNotes/Icehouse#Upgrade_Notes_5

[Anne Gentle (annegentle)]

I don't find any place to talk about this in API reference docs.