#3340 - Adding support for 0ms push timeout for blocking mailboxes
Shutdown ordering issue in RemoteDeploymentDeathWatchSpec, see #3334
Remove some unnecessary object creation and switch to HashSet for better performance. See #3308
Hardening of cluster member leaving path, see #3309

* Removed leader commands for Shutdown and Exit
* Member shutdown itself  when it sees itself as Exiting
* Singleton cluster with status Exiting will shutdown itself,
  in case the Exiting gossip never arrives
* Exiting member not part convergence check
* Exiting member is removed by leader (on convergence) when the
  exiting member is in the unreachable set, i.e. sucessfully shutdown
* Reverted the change made for #3266, i.e. Exiting is
  detected as unreachable again.
* Adjust ClusterSingletonManager to new Exiting behaviour
* Fix bug in HeartbeatSender, which caused it to continue to
  send heartbeats to removed nodes, instead of rebalancing
* Refactoring of leaderActions method
* Leaving section in docs
Merge pull request #1441 from akka/wip-3308-actorsystemspec-times-out-ban

ActorSystemSpec timeout fixes #3308
Remove auto-join config, derive from seed-nodes, see #3359
Merge pull request #1432 from akka/wip-3309-exiting-patriknw

Hardening of cluster member leaving path, see #3309
Merge pull request #1443 from akka/wip-3359-auto-join-patriknw

Remove auto-join config, derive from seed-nodes, see #3359
Merge pull request #1444 from akka/wip-3334-RemoteDeploymentDeathWatchSpec-patriknw

Shutdown ordering issue in RemoteDeploymentDeathWatchSpec, see #3334
Merge pull request #1436 from akka/wip-3340-0-push-timeout-√

 #3340 - Adding support for 0ms push timeout for blocking mailboxes
Missing barrier coordination in RemoteNodeDeathWatchSpec, see #3350
Merge pull request #1445 from akka/wip-3340-RemoteNodeDeathWatchSpec-patriknw

Missing barrier coordination in RemoteNodeDeathWatchSpec, see #3340