Fix NovaObject versioning attribute usage

A typo made early in the object prototyping process has meant that
all objects thus far have been exposing a version of '1.0' because
the base object has been using an attribute of 'version'. The
object implementations have been exposing a 'VERSION' attribute
with their desired version advertisement.

Since we are still relatively early in the process of deploying
objects, the impact from this should be relatively minor, although
it is important to get this fixed ASAP before any incompatible
object changes are made.

(cherry picked from commit 99cbfb3492c80ded53fa018fe5a0881f977dc407)

Change-Id: If9154dc663111f304f72ef7f6f37c465e84ff504
Closes-bug: #1239709
Merge "Fix NovaObject versioning attribute usage" into stable/havana