Update Nova to allow using either Glance V1 or V2 API

This involved more than just setting the desired version number
in the image service because the workflow and values aren't
necessarily the same betwee V1 and V2, so a driver layer was
introduced that acts as an adapter between the image service
class and the actual Glance client.

Implements: bp use-glance-v2-api

Change-Id: Ie39cb541139e2bc65d844e17363cb1dc1fa3791e