Indicate when nodes are being stopped in the network stress test

It may help distinguish errors derived from forcibly stopping nodes (e.g. after a timeout).

network/src/test/java/io/bitsquare/p2p/network/NetworkStressTest.java

@@ -228,6 +228,8 @@ public class NetworkStressTest {
 
     @After
     public void tearDown() throws InterruptedException, IOException {
+        print("stopping all local nodes");
+
         /** A barrier to wait for concurrent shutdown of services. */
         final CountDownLatch shutdownLatch = new CountDownLatch((seedNode != null? 1 : 0) + peerNodes.size());