cyclades: Fix issue with storing images

The 'get_or_create' method should be used only for the 'uuid' and
'version' parameters.  Otherwise, any change of the image (e.g.
location) would cause the creation of a new image which would result in
integrity error.
cyclades: Pass the size of volume's origin

..to Archipelago, as 'origin_size' parameter.

Currently, the volume object is annotated with the size of the origin,
but this information is not stored in DB. This will have to be changed
when Synnefo supports detachable volumes.
cyclades: Fix wrong import