Thread factory provided by the client should be used if not null (AsyncHttpClient#1545)

* thread factory provided by the client should be used if not null, as being done in ChannelManager

* Restoring the behavior for fallback, with "-timer" in the name.

Author: waleed-dawood

client/src/main/java/org/asynchttpclient/DefaultAsyncHttpClient.java

@@ -92,7 +92,8 @@ public DefaultAsyncHttpClient(AsyncHttpClientConfig config) {
   }
 
   private Timer newNettyTimer(AsyncHttpClientConfig config) {
-    ThreadFactory threadFactory = new DefaultThreadFactory(config.getThreadPoolName() + "-timer");
+    ThreadFactory threadFactory = config.getThreadFactory() != null ? config.getThreadFactory() : new DefaultThreadFactory(config.getThreadPoolName() + "-timer");
+
     HashedWheelTimer timer = new HashedWheelTimer(threadFactory);
     timer.start();
     return timer;