do not generate schema each time get_schema is called

[Aaron Rosen]

Previously each time one called get_schema() on a datasource_driver we would
generate it by walking through all of the translators. This patch changes the
logic so that we store the schema when we register a datasource so we do not
have to generate it each time. Note: the schema never changes durring run time
so we're able to cache it like this.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/150582
Committed: https://git.openstack.org/cgit/stackforge/congress/commit/?id=9cf02c7bde5ef4926bda10631c40cf978992d020
Submitter: Jenkins
Branch: master

commit 9cf02c7bde5ef4926bda10631c40cf978992d020
Author: Aaron Rosen <email address hidden>
Date: Tue Jan 27 12:48:41 2015 -0800

    Cache schema generation

    Previously each time one called get_schema() on a datasource_driver we would
    generate it by walking through all of the translators. This patch changes the
    logic so that we store the schema when we register a datasource so we do not
    have to generate it each time. Note: the schema never changes durring run time
    so we're able to cache it like this.

    Change-Id: I4deead9fa698e681c0f0a8f07a4ef7d95726bae7
    Closes-bug: #1415208