MidNet plugin should be validating against unsupported provider_network_type

[Tomoe Sugihara]

Currently, arbitrary string goes through the API and users would not notice an error if they have a typo.

[YAMAMOTO Takashi (yamamoto)]

https://github.com/openstack/networking-midonet/blob/cac1ba23d89837479deed28838eee354a3163c1d/midonet/neutron/db/provider_network_db.py#L64-L73

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/237474

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/237474
Committed: https://git.openstack.org/cgit/openstack/networking-midonet/commit/?id=70f26781946fd60f68b9e95ab537644a67471861
Submitter: Jenkins
Branch: master

commit 70f26781946fd60f68b9e95ab537644a67471861
Author: YAMAMOTO Takashi <email address hidden>
Date: Tue Oct 20 17:46:27 2015 +0900

    plugin_v2: Tighten network_type validation a bit

    Instead of accepting any values, accept ours (midonet, uplink)
    and what currently Horizon can send us without any attributes.
    (local)

    Closes-Bug: #1486943
    Change-Id: Ib7824cda521393167771dee06baa6a23d88ac134