Adding support for Coraid AoE SANs Appliances.

Adding support for Coraid AoE SANs Appliances.

This driver provide support for Coraid hardware storage appliances
using AoE (ATA Over Ethernet) protocol.

Implements blueprint coraid-volume-driver

Reference to Nova patch libvirt-aoe :
https://review.openstack.org/21101

The following operations are supported :
-- Volume Creation with Volume Types
-- Volume Deletion
-- Volume Attach
-- Volume Detach
-- Snapshot Creation
-- Snapshot Deletion
-- Create Volume from Snapshot
-- Volume Stats

The driver only work when operating on EtherCloud ESM,
Coraid VSX and Coraid SRX Appliances.

Change-Id: I7c8dde0c99698b52c151a4db0fb1bb94d516db61