can discover addresses when dynamic port assignment (bind to port 0)
  is used. This could, for example, be used to update address
  information in a ZooKeeper database.

- Client storagers have a method, new_addr, that can be used to change
  the server address(es). This can be used, for example, to update a
  dynamically determined server address from information in a
  ZooKeeper database.

- Moved some responsibility from runzeo to StorageServer to make it
  easier to use storage servers without runzeo.