Occasional unclean stop(), primarily when tearing down Http actors

[tolbertam]

Occasionally in testing, and usually on the first instance I tear down, I see logs after stopping an Scassandra instance:

    3247   [Scassandra-akka.actor.default-dispatcher-11] INFO  spray.can.server.HttpListener - Unbound from /127.0.1.1:53191
    3251   [Scassandra-akka.actor.default-dispatcher-8] INFO  akka.actor.DeadLetterActorRef - Message [scala.concurrent.impl.Promise$DefaultPromise] from Actor[akka://Scassandra/user/$a#142876029] to Actor[akka://Scassandra/deadLetters] was not delivered. [1] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3251   [Scassandra-akka.actor.default-dispatcher-8] INFO  akka.actor.LocalActorRef - Message [akka.actor.Terminated] from Actor[akka://Scassandra/user/$a/PrimingServer/$a#-2106721686] to Actor[akka://Scassandra/user/IO-HTTP/listener-0/0#26064141] was not delivered. [2] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3252   [Scassandra-akka.actor.default-dispatcher-8] INFO  akka.actor.LocalActorRef - Message [akka.dispatch.sysmsg.Terminate] from Actor[akka://Scassandra/user/$a/PrimingServer#1458845999] to Actor[akka://Scassandra/user/$a/PrimingServer#1458845999] was not delivered. [3] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3253   [Scassandra-akka.actor.default-dispatcher-14] INFO  akka.actor.LocalActorRef - Message [akka.dispatch.sysmsg.Terminate] from Actor[akka://Scassandra/user/$a/BinaryTcpListener/$b#1257390532] to Actor[akka://Scassandra/user/$a/BinaryTcpListener/$b#1257390532] was not delivered. [4] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3256   [Scassandra-akka.actor.default-dispatcher-12] INFO  spray.can.server.HttpListener - Unbound from /127.0.1.2:53191
    3257   [Scassandra-akka.actor.default-dispatcher-12] INFO  akka.actor.LocalActorRef - Message [akka.dispatch.sysmsg.DeathWatchNotification] from Actor[akka://Scassandra/user/IO-HTTP/listener-1/0#-885437980] to Actor[akka://Scassandra/user/IO-HTTP/listener-1/0#-885437980] was not delivered. [5] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3257   [Scassandra-akka.actor.default-dispatcher-12] INFO  akka.actor.DeadLetterActorRef - Message [scala.concurrent.impl.Promise$DefaultPromise] from Actor[akka://Scassandra/user/$b#1358713893] to Actor[akka://Scassandra/deadLetters] was not delivered. [6] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3301   [Scassandra-akka.actor.default-dispatcher-8] INFO  akka.actor.LocalActorRef - Message [spray.io.TickGenerator$Tick$] from Actor[akka://Scassandra/deadLetters] to Actor[akka://Scassandra/user/IO-HTTP/listener-0/0#26064141] was not delivered. [7] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.
    3493   [Scassandra-akka.actor.default-dispatcher-4] INFO  akka.actor.LocalActorRef - Message [spray.io.TickGenerator$Tick$] from Actor[akka://Scassandra/deadLetters] to Actor[akka://Scassandra/user/IO-HTTP/listener-1/0#-885437980] was not delivered. [8] dead letters encountered. This logging can be turned off or adjusted with configuration settings 'akka.log-dead-letters' and 'akka.log-dead-letters-during-shutdown'.

This isn't really a problem, but the order of how things get cleaned up must be inconsistent/wrong. Some of these messages may not hard to avoid (i.e. the Tick message) being sent after the actor is killed, but others like messages derived from Promises (must be using Ask somewhere?) could be unneeded.