EndpointPolicy backend implementation doesn't inherit its driver interface

[Harini]

Every backend implemented in sql.py files, inherit the respective driver interface class.
But EndpointPolicy backend implementation defined @ 'keystone/endpoint_policy/backends/sql.py' file is anomalous.
It doesn't inherit its driver interface. So, fix it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/352586

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/352586
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=97585c15a62eb081cce5489bf4b91f0ee0334fcb
Submitter: Jenkins
Branch: master

commit 97585c15a62eb081cce5489bf4b91f0ee0334fcb
Author: Harini <email address hidden>
Date: Tue Aug 9 01:40:18 2016 +0530

    EndpointPolicy driver doesn't inherit interface

    Added the driver interface 'base.EndpointPolicyDriverV8' as super class
    of the sql driver implementation.

    Removed unused methods from driver interface and added release notes.

    Change-Id: I198dcbda7591e0dafb1da3a72e3f32b258c0e299
    Closes-Bug: #1611102

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/keystone 11.0.0.0b1 development milestone.