Adding a `refetchOnExpiry` method to be overridable in subclasses
Adding a `refetchOnExpiry` method to be overridable in subclasses

We need the ability to conditionally kill or stagger refetches on
expiry. This method can be used for that in an Em.Resource or
Em.ResourceCollection extension or in a subclass.

zendesk/ember-resource,zendesk/ember-resource