Brightbox : Include licence_name in Image

Also update test helper

lib/fog/brightbox/models/compute/image.rb

@@ -20,6 +20,7 @@ module Fog
         attribute :arch
         attribute :virtual_size
         attribute :disk_size
+        attribute :licence_name
 
         # Boolean flags
         attribute :public

tests/brightbox/requests/compute/helper.rb

@@ -530,6 +530,7 @@ class Brightbox
           "server_groups"   => [Brightbox::Compute::Formats::Nested::SERVER_GROUP],
           "interfaces"      => [Brightbox::Compute::Formats::Nested::INTERFACE],
           "zone"            => Fog::Brightbox::Nullable::Zone,
+          "licence_name"    => String,
           "username"        => Fog::Nullable::String
         }