Add experimental and hacky support for authenticating against Keystone API v3
via OpenStack based drivers.

Notes:

1. Domains are not supported yet
2. Projects are supported by specifying "ex_tenant_name" argument
3. Internal interface is subject to change and will change in the near future
Make get_regions work with v3 auth.
Add utility get_service_types method to OpenStackServiceCatalog class.
Add two missing super calls.
Add initial implementation of a base networking API with a reference drivers
for OpenStack Neutron and OpenStack Quantum.

Also add support for retrieving a networking driver to the OpenStack compute
driver.

Note: Base API hasn't been decided upon yet and is subject to change.