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

cinder/volume/volume_types.py

@@ -143,3 +143,16 @@ def is_key_value_present(volume_type_id, key, value, volume_type=None):
         return False
     else:
         return True
+
+
+def get_volume_type_extra_specs(volume_type_id, key=False):
+    volume_type = get_volume_type(context.get_admin_context(),
+                                  volume_type_id)
+    extra_specs = volume_type['extra_specs']
+    if key:
+        if extra_specs.get(key):
+            return extra_specs.get(key)
+        else:
+            return False
+    else:
+        return extra_specs