Refactor metadef ORM as_dict method to to_dict for consistency

[Wayne]

The Metadef ORM classes should refactor as_dict to to_dict to be consistent with other glance ORM classes.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/121836

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/121836
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=7baa3d9ff8361fe87e0597486c8905338b4901fd
Submitter: Jenkins
Branch: master

commit 7baa3d9ff8361fe87e0597486c8905338b4901fd
Author: Wayne Okuma <email address hidden>
Date: Tue Sep 16 02:40:44 2014 -0700

    Refactor metadef ORM classes to use to_dict instead of as_dict

    The Metadef ORM base dictionary class should replace as_dict with to_dict
    to be consistent with other Glance ORM classes.

    Change-Id: I1550bd519f100cdffcf5046e9838cf192d4aac50
    Closes-Bug: 1370058