Add cinder volume driver for Blockbridge EPS

Add cinder volume driver for Blockbridge EPS

This initial commit includes support for the minimum required volume
operations:

- Volume Create/Delete
- Volume Attach/Detach
- Snapshot Create/Delete
- Create Volume from Snapshot
- Get Volume Stats
- Copy Image to Volume
- Copy Volume to Image
- Clone Volume
- Extend Volume

For more details about our storage backend, please see the blueprint.

blueprint blockbridge-eps-driver
Change-Id: I99c95243bec708c6519cb69c4cb68085ad698c83