The HeartbeatProvider needs to get updated every time the endpoint sends a heartbeat

relates to:
https://github.com/Particular/ServiceControl/pull/276
This relates to Particular/ServicePulse#104

@andreasohlund - Since the heartbeat provider is never updated with the heartbeat information, the logic for marking the endpoints dead was not happening. i.e. Endpoints won't be reported dead.

Please code review and merge.