EndpointFilter backend implementation doesn't inherit its driver interface

[Vivek Dhayaal]

Every backend implemented in sql.py/kvs.py/... files, inherits the respective driver interface class.
But EndpointFilter backend implementation specified @ 'keystone/contrib/endpoint_filter/backends/sql.py' file is anomalous.
It doesn't inherit the driver interface. This could lead to methods specified in interface not being implemented in the drivers and subsequent runtime issues when such methods are invoked. So, fix it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/213342

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/213342
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=5b2d86fd3360db6ff2c7b135137291d78c76bb03
Submitter: Jenkins
Branch: master

commit 5b2d86fd3360db6ff2c7b135137291d78c76bb03
Author: Vivek Dhayaal <email address hidden>
Date: Fri Aug 14 21:00:58 2015 +0000

    EndpointFilter driver doesnt inherit its interface

    Added 'endpoint_filter.Driver' as super class of the sql driver implementation

    Change-Id: I1966d89a5f9b3c4c5ef5d9ad6709fc06cbe0c1f7
    Closes-Bug: #1485116