API Extension for Tenant Networks

The os-networks extension is intended to be admin only, and in that capacity, does things only an admin should be allowed to do, like list all known networks. I'd like to propose renaming that extension to os-admin-networks and supplying a new extension focused on tenants to take over the os-networks namespace. Alternatively, I think it would be acceptable to supply the tenant only extension under the name os-tenant-networks and leave the existing networks extension alone.

This blueprint also strongly asserts the need for things that are "extensions" to stop requiring changes in novaclient. Namely, network "extension" changes recently went into novaclient that essentially make assumptions about existence of extensions in the API.