Wait for akka termination in test

We now correctly close the test classloader which can cause this
scripted test to fail if the classloader is closed before the actor
system finishes terminating.

sbt/src/sbt-test/tests/scala-instance-classloader/src/test/scala/Test.scala

@@ -1,6 +1,8 @@
 package akka.actor
 
 import org.junit._
+import scala.concurrent._
+import scala.concurrent.duration._
 
 class BadTest {
 
@@ -13,7 +15,7 @@ class BadTest {
     val system = ActorSystem()
     def evilGetThreadExectionContextName =
       system.asInstanceOf[ActorSystemImpl].internalCallingThreadExecutionContext.getClass.getName
-    system.terminate()
+    Await.result(system.terminate(), 5.seconds)
     val expected = "scala.concurrent.Future$InternalCallbackExecutor$"
     Assert.assertEquals("Failed to grab appropriate Akka name", expected, evilGetThreadExectionContextName)
   }