mark properties as deleted if they don't exist on an update

[Dan Prince]

When using the glance client to update an image the metadata (aka 'properties') items not marked as deleted if they no longer exist.

As an example. If I were to created an image with properties:

  'properties': {'distro': 'Ubuntu 10.04 LTS', 'arch': 'x86_64'}

And then update the image with properties:

  'properties': {'arch': 'x86_64'}

I would expect a subsequent call to get the image detail to return only {'arch': 'x86_64'}. This is not currently what happens.