Require List objects to be able to backlevel their contents

Right now, a client declares its supported version of a given object
automatically in the remoted calls it makes to conductor. However,
in the case of things like InstanceList.get_by_foo(), they are
reporting the version of their InstanceList object, not their
Instance object. Conductor fills a version-matching InstanceList
object with brand new Instance objects, which the client, of course,
barfs on.

There may be a better way to handle this going forward, but for now,
stop the bleeding by requiring a version bump to the corresponding
List object whenever the object type it contains takes a version
bump. This adds a test to validate that all the objects registered
have a suitable mapping for the current version in the tree.

Since this actually caused a breakage in the Instance object
recently, this also bumps the InstanceList version so that
conductors running this commit (or later) will properly send
version 1.9 Instance objects to Havana clients and version 1.10+
to newer ones.

Change-Id: I2668dead4784fbd0411d1b6372a9a8006eeb2e84
Related-Bug: #1258256
Closes-Bug: #1254902

nova/objects/aggregate.py

@@ -147,11 +147,17 @@ class Aggregate(base.NovaPersistentObject, base.NovaObject):
 class AggregateList(base.ObjectListBase, base.NovaObject):
     # Version 1.0: Initial version
     # Version 1.1: Added key argument to get_by_host()
+    #              Aggregate <= version 1.1
     VERSION = '1.1'
 
     fields = {
         'objects': fields.ListOfObjectsField('Aggregate'),
         }
+    child_versions = {
+        '1.0': '1.1',
+        '1.1': '1.1',
+        # NOTE(danms): Aggregate was at 1.1 before we added this
+        }
 
     @base.remotable_classmethod
     def get_all(cls, context):