The variable '_hash_rings' is being referenced by both
self.__class__._hash_rings (for assigning) and self._hash_rings (for
reading).
Instead use only self.__class__._hash_rings to be consistent. This
should be less confusing. Before the reader had to know the scoping
rules and that reading self._hash_rings was actually reading
self.__class__._hash_rings. But assigning to self._hash_rings would
create a new instance variable instead of updating the class level
self.__class__._hash_rings.
This change will hopefully make the code easier to read and understand.
Change-Id: I6c38962ee6c8d6b341a04efaffa8e7a0f53bfbe5
874b54d478