* Added publishCurrentClusterState and sendCurrentClusterState
* Removed Ping/Pong that was used for some tests, since awaitCond is
now needed anyway, since publish to eventStream is done afterwards
* Major refactoring to remove the need to use special
Cluster instance for testing. Use default Cluster
extension instead. Most of it is trivial changes.
* Used failure-detector.implementation-class from config
to swap to Puppet
* Removed FailureDetectorStrategy, since it doesn't add any value
* Added Cluster.joinSeedNodes to be able to test seedNodes when Addresses
are unknown before startup time.
* Removed ClusterEnvironment that was passed around among the actors,
instead they use the ordinary Cluster extension.
* Overall much cleaner design
* Gossip is not exposed in user api
* Better and more events
* Snapshot event sent to new subscriber
* Updated tests
* Periodic publish only for internal stats
* Essentially as already described in cluster specification,
but now fully implemented and tested with LargeClusterSpec
* Gossip to nodes with different view (using seen table)
with certain probability
* Gossip chat, gossip back to sender
* Immediate gossip to joining node
* Updated some tests to reflect current implementation
* Add new operators :+ and :++ by implicit conversion
* Unfortunately this means that we must remember to use
these until SI-5986 is fixed. Is there a better way?
