* 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
* Add some more logging to be able to diagnose eventual problems
* Explicit config of nr-of-end-heartbeats
- Asynchronous lockless remoting
- Pluggable transport drivers
- Multiple transport support
- Simplified lifecycle events
- Support for netty based TCP, SSL+TCP and UDP support
- Updated Akka protocol with soft-state connections and failure detection
- Refactored failure detectors (currently duplicated from cluster)
