Add a Quobyte Volume Driver in Nova

Add a Nova volume driver for Quobyte Unified Storage Plane,
allowing to attach vm images residing
in Quobyte USP to Nova instances. These images (raw, qcow2) are stored as
files on a Quobyte USP volume.

Blueprint: quobyte-nova-driver

Change-Id: Ibe97ba82d017a95bc0a6621b07fe971885b35373