Convert java.net.UnknownHost to a Ruby exception, update test expectations
Make blocking consumers gracefully shutdown when there were no deliveries

By injecting a poision element into the internal queue we make
sure that even if there were no deliveries, we still can unblock
and not wait on LinkedBlockedQueue#take forever.
Add HotBunnies::Channel#connection that returns HB::Session

Otherwise it will return the Java connection via method_missing.