recovery: ensure we always have a replica object for self
recovery: ensure we always have a replica object for self

Ensure we always have at least "self" in the replication cluster
(replica set), even if replication is off.

The local instance can never be removed from the replica set.

This simplifies further reasoning about the code.

rtsisyk/tarantool,rtsisyk/tarantool,rtsisyk/tarantool,rtsisyk/tarantool