get_known_ipaddrs_of_cluster adds empty clusters to the cluster manager state [JIRA: RIAK-2354]

[ian-mi]

Every call of get_known_ipaddrs_of_cluster reorders the members of the cluster in the cluster manager state. I seems somewhat questions that this function modifies the state at all, but it should at least leave the state unchanged modulo the the order of the cluster's members. However, when called on a cluster which is not currently known to the connection manager, that cluster will be added to the connection manager state with no members. Instead I think the state should simply be left unchanged.

This issue manifests itself when stale connections caused disconnected cluster to be readded to the cluster manager state as the riak_repl locator calls get_known_ipaddrs_of_cluster. This can cause the cluster to reappear in the riak-repl status immediately after calling riak-repl disconnect.