cinder_img_volume_type image metadata ignored in Train

[Tony P]

In Train, when launching an instance through horizon, from an image and creating a new volume; the glance image metadata `cinder_img_volume_type` is set to select a Volume-Type (which then sets a volume backend). Discovered with Train, the volume type is not selected but instead the default or `__DEFAULT__`.

Steps to reproduce:
1. Install packstack Train

2. Update cinder.conf with enabled_backends and the [backend] (need to restart cinder services)

3. Log in to Openstack Add the volume type to reference the backend (for reference, I call this volume type `number-1`)

4. Upload an image and add metadata `cinder_img_volume_type` and the name as mentioned in step 3: number-1

5. Try and create an instance using horizon. Source = image and create new volume

6. Result = volume type / backend as set in the image metadata is not used and instance goes into error status.

If you repeat the above steps under Stein, the issue is not present and the correct volume type is selected based on the glance image metadata.