Detect failure when no heartbeats sent, see #2907

* Subscribe to InstantMemberEvent and start heartbeating when
  InstantMemberUp. Same for metrics.
* HeartbeatNodeRing data structure for bidirectional mapping of
  heartbeat sender and receiver. Not using ConsistentHash anymore.
  Node addresses are hashed to ensure that neighbors are spread out.
* HeartbeatRequest when receiver detects that it has not received
  expected heartbeats.
* New test InitialHeartbeatSpec that simulates the problem
* Add/remove some related conf properties

There might be a regression in StressSpec, or this new code triggers some new usage patterns of the remoting. I will investigate that more, but in the meantime we can start the review process of this PR.