(PCP-357) Don't start heartbeat task before connecting
(PCP-357) Don't start heartbeat task before connecting

Adding the start-heartbeat-task to the Client interface; it will be up
to the client code to actually start the heartbeat task to keep the
WebSocket connection up.

Removing the call that starts the heartbeat task right before spawning
the make-connection thread (in the 'connect' function).

puppetlabs/clj-pcp-client