=sam #16905 multiple fixes for java-lambda doc samples

* use a free port instead of a hardcoded one
* do not use null for stream elements
* use defined java8 home key

akka-docs-dev/rst/scala/code/docs/utils/TestUtils.scala

@@ -0,0 +1,24 @@
+/**
+ * Copyright (C) 2009-2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+
+package docs.utils
+
+import java.net.InetSocketAddress
+import java.nio.channels.ServerSocketChannel
+
+object TestUtils {
+  def temporaryServerAddress(interface: String = "127.0.0.1"): InetSocketAddress = {
+    val serverSocket = ServerSocketChannel.open()
+    try {
+      serverSocket.socket.bind(new InetSocketAddress(interface, 0))
+      val port = serverSocket.socket.getLocalPort
+      new InetSocketAddress(interface, port)
+    } finally serverSocket.close()
+  }
+
+  def temporaryServerHostnameAndPort(interface: String = "127.0.0.1"): (String, Int) = {
+    val socketAddress = temporaryServerAddress(interface)
+    socketAddress.getHostName -> socketAddress.getPort
+  }
+}