EUCA-7074
Stuck on this one, will come back to it later. For some reason when a model in the instance collection changes, all the other models lose track of the 'changed' status they held, so at the end when we look for changed models in the collection only the last one changed returns true from the hasChanged() call.

Test:
- set a breakpoint on this file at line 109 or so
- open the scaling groups manage instances dialog on a group with several instances in it
- get hold of the collection and the instances in it in your debugging console:

--> c = scope.sgroup.get('instances'); m0 = c.at(0); m1 = c.at(1); m2 = c.at(2);

- Then set something on one of the models and verify the change status:

--> m0.set('x', true);
--> m0.changed

- Now set something in another model, and check m0 again...

--> m1.set('y', true);
--> m1.changed
--> m0 changed

- ...and so on. Only the last one changed keeps its changed status.
EUCA-7074
Simple solution - Backbone doesn't keep a model change history around forever, so you have to track that yourself if it's important to you, as it is here.
Merge branch 'testing-3.3' into maint/3.3/testing