Remove the `ip_addr` column which was not used. IP addresses are not
part of Raft configuration now and they can change dynamically.
Swap the `server_id` and `disposition` columns in the clustering key, so
when querying the configuration, we first obtain all servers with the
current disposition and then all servers with the previous disposition
(note that a server may appear both in current and previous).
2bfe85ce9b