tenantattr extension for cinder; ExtractInto method for handling custom Volume objects
diff --git a/openstack/blockstorage/v2/volumes/results.go b/openstack/blockstorage/v2/volumes/results.go
index 2ad94cd..0f39fdb 100644
--- a/openstack/blockstorage/v2/volumes/results.go
+++ b/openstack/blockstorage/v2/volumes/results.go
@@ -1,6 +1,8 @@
 package volumes
 
 import (
+	"encoding/json"
+
 	"github.com/gophercloud/gophercloud"
 	"github.com/gophercloud/gophercloud/pagination"
 )
@@ -100,6 +102,22 @@
 	return s.Volume, err
 }
 
+func (r commonResult) ExtractInto(v interface{}) error {
+	var vol map[string]map[string]interface{}
+	err := r.ExtractInto(&vol)
+	if err != nil {
+		return err
+	}
+
+	b, err := json.Marshal(vol["volume"])
+	if err != nil {
+		return err
+	}
+
+	err = json.Unmarshal(b, &v)
+	return err
+}
+
 // CreateResult contains the response body and error from a Create request.
 type CreateResult struct {
 	commonResult