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