Correcting description of image_update API method.
Correcting description of image_update API method.

Currently, the description refers to the method returning:
    "a dictionary representation of a newly created *Image* object"
This is probably copy-pasted from image_create.
Updated database_architecture.rst to say:
    "a dictionary representation of the updated *Image* object"

Change-Id: Ie3101fa6c17bd6c62958543c327964c9e85f428a

openstack/glance,rajalokan/glance,openstack/glance,openstack/glance,stevelle/glance,stevelle/glance,rajalokan/glance