Increase timeout on Netty client latch for tests

We use a latch when sending requests during tests so that we do not hang
forever waiting for replies on those requests. This commit increases the
timeout on that latch to 30 seconds because sometimes 10 seconds is just
not enough.

modules/transport-netty4/src/test/java/org/elasticsearch/http/netty4/Netty4HttpClient.java

@@ -144,7 +144,7 @@ class Netty4HttpClient implements Closeable {
             for (HttpRequest request : requests) {
                 channelFuture.channel().writeAndFlush(request);
             }
-            latch.await(10, TimeUnit.SECONDS);
+            latch.await(30, TimeUnit.SECONDS);
 
         } finally {
             if (channelFuture != null) {