Add generic block device driver

Add generic block device driver

This driver adds an ability to create volumes on any block device on
local host.

This driver supports the following features:

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

Not implemented:

- Snapshot Create/Delete
- Create Volume from Snapshot

These features are not implemented because there is no generic way
to create snapshots for block devices.

bp block-device-driver

Change-Id: If5fcaf2775daf660c46d630eea0f9633ca816ee9