Make Object FieldType from_primitive pass objects

In case we have a ListOfObjects field on an object with a remotable
method, due to NovaObjectsSerializer now looking into dicts recursively,
and thus also into the updates dict that object_action returns,
it is possible that objects inside a list have already been
deserialized, so we make the Fields from_primitive just pass them on,
since the job was already done by the NovaObjectsSerializer.

Change-Id: Ib2a34a115cb2d0a2a0765c81d5dd7ef331077eb5
Closes-bug: #1360656
Merge "Make Object FieldType from_primitive pass objects"