Cannot create instances from snapshots of images.

Issue

• Take a snapshot of a working instance.
• Attempt to launch a new instance from that snapshot.
• Observe the following error in nova-compute.log:

2015-07-21 12:10:42.919 14518 ERROR nova.compute.manager [req-f398f914-02cb-4965-9752-521ed98163b4 - - - - -] [instance: <uuid>] Instance failed to spawn
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>] Traceback (most recent call last):
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2442, in _build_resources
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     yield resources
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/compute/manager.py", line 2314, in _build_and_run_instance
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     block_device_info=block_device_info)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 2421, in spawn
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     admin_pass=admin_password)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 2832, in _create_image
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     instance, size, fallback_from_host)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 5973, in _try_fetch_image_cache
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     size=size)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/imagebackend.py", line 231, in cache
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     *args, **kwargs)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/imagebackend.py", line 755, in create_image
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     prepare_template(target=base, max_size=size, *args, **kwargs)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/oslo_concurrency/lockutils.py", line 445, in inner
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     return f(*args, **kwargs)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/imagebackend.py", line 221, in fetch_func_sync
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     fetch_func(target=target, *args, **kwargs)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/driver.py", line 2824, in clone_fallback_to_fetch
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     backend.clone(context, disk_images['image_id'])
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/virt/libvirt/imagebackend.py", line 780, in clone
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     include_locations=True)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/image/api.py", line 93, in get
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     show_deleted=show_deleted)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/image/glance.py", line 301, in show
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     _reraise_translated_image_exception(image_id)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/image/glance.py", line 299, in show
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     image = self._client.call(context, version, 'get', image_id)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/nova/image/glance.py", line 219, in call
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     return getattr(client.images, method)(*args, **kwargs)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/glanceclient/v2/images.py", line 177, in get
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     return self.model(**body)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/warlock/core.py", line 32, in __init__
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     base_class.__init__(self, *args, **kwargs)
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]   File "/usr/lib/python2.7/site-packages/warlock/model.py", line 34, in __init__
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     raise ValueError(str(exc))
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>] ValueError: None is not of type u'string'
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>] 
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>] Failed validating u'type' in schema[u'properties'][u'ramdisk_id']:
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     {u'description': u'ID of image stored in Glance that should be used as the ramdisk when booting an AMI-style image.',
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]      u'is_base': False,
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]      u'pattern': u'^([0-9a-fA-F]){8}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){4}-([0-9a-fA-F]){12}$',
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]      u'type': u'string'}
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>] 
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>] On instance[u'ramdisk_id']:
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]     None
2015-07-21 12:10:42.919 14518 TRACE nova.compute.manager [instance: <uuid>]