Comment 1 for bug 1532078

We assume by design that the AZ information is only a specific key/value pair of the metadata dict (where the key is 'availability_zone').

Trying to access the AZ info if the metadata field is unset goes against that design decision because it makes no sense to persist it differently at the object layer. Having a level of indirection for accessing it doesn't mean we should have a defensive approach for accessing that information.