Change prep_resize paths to use objects

Converts calls to compute's prep_resize to pass a new-world instance
object.

This does not convert the scheduler prep_resize method which is still
called on reschedules.  It will soon be deprecated anyway.

Related to blueprint unified-object-model

Change-Id: I7a150f119547595aec962d5e5a8d2ab815d0b6c5

nova/conductor/manager.py

@@ -676,7 +676,7 @@ class ComputeTaskManager(base.Base):
 
             (host, node) = (host_state['host'], host_state['nodename'])
             self.compute_rpcapi.prep_resize(
-                context, image, nova_object.obj_to_primitive(instance),
+                context, image, instance,
                 flavor, host,
                 reservations, request_spec=request_spec,
                 filter_properties=filter_properties, node=node)