Add reconnect logic to the relay

Upgrade to Reactor snapshot builds to take advantage of TcpClient's
reconnect support that was added post-M1. Now, if the broker fails after
an initial successful connection the broker will attempt to reconnect
every 5 seconds.

A more sophisticated reconnection policy, including back off and
failover to different broker are possible with the Reactor API. We may
want to enhance the relay's reconnection policy in the future.