Comment 11 for bug 1444841

So having talked to bauzas about this a bit, it seems like instance.az should go away. Instead, all code should refer to instance.host.az (accepting that this may not be set immediately) and/or the instance's request_spec.az. Sylvain is still working on getting request spec committed and has a giant tail of patches on that already. He says alaski will provide a means of looking up the request spec for an instance. Once that is available we can get rid of the get_instance_availability_zone method entirely.