Allow client port to support plaintext and encrypted connections simultaneously

ZOOKEEPER-2125 extended the ZooKeeper server-side to handle encrypted client connections by allowing the server to open a second client port (the secure client port) to manage this new style of traffic. A server is able to handle plaintext and encrypted clients simultaneously by managing each on their respective ports.

When it comes time to get all clients connecting to your system to start using encryption, this approach requires that they make two changes simultaneously: altering their client properties to start use the secure settings and altering the routing information that they provide in order to know where to connect with the ensemble. If either is misconfigured then the client is cut off from the ensemble. With a large deployment of clients that are owned by a different teams and different tools, this presents a danger in activating the feature. Ideally, the two changes could be staggered so that first the encryption feature is activated and then the routing information is changed in a subsequent phase.

Allow the server connection factory managing the regular client port to handle both plaintext and encrypted connections. This will be independent of the operation of the server connection factory managing the secure client port but similar settings ought to apply to both (e.g. cipher suites) to maintain inter compatibility.