/versions endpoint returns 300 everytime

[Flavio Percoco]

The /versions endpoint returns a 300 status code even when the user explicitly asks for the version list. This is confusing and not the desired behavior since there's just 1 choice for the `/versions` endpoint.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/219649

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/219649
Committed: https://git.openstack.org/cgit/openstack/glance/commit/?id=3fc253c197095f5f09846855a755b677ec37deb5
Submitter: Jenkins
Branch: master

commit 3fc253c197095f5f09846855a755b677ec37deb5
Author: Flavio Percoco <email address hidden>
Date: Wed Sep 2 13:16:24 2015 +0200

    Don't return 300 when requesting /versions

    Whenever the versions resource is used, it'll reply with a 300 status
    code. This is the desired behavior when requesting versions that we
    don't support and/or non-existent.

    However, when the user requests specifically for the `/versions`
    endpoint, Glance shouldn't reply with a 300 since there's just 1 choice
    for such endpoint.

    APIImpact
    Closes-bug: #1491350

    Change-Id: I23e3780e5d1b609753ffef59418115f45ab45fe7