Simplify calculation of shutdown timeout

Fixes #194

Author: acogoluegnes

src/main/java/com/rabbitmq/client/impl/AMQConnection.java

@@ -393,7 +393,7 @@ public void start()
     protected ChannelManager instantiateChannelManager(int channelMax, ThreadFactory threadFactory) {
         ChannelManager result = new ChannelManager(this._workService, channelMax, threadFactory, this.metricsCollector);
         result.setShutdownExecutor(this.shutdownExecutor);
-        result.setChannelShutdownTimeout((int) (requestedHeartbeat * 1000.0 + requestedHeartbeat * 1000.0 * (5.0 / 100.0)));
+        result.setChannelShutdownTimeout((int) ((requestedHeartbeat * 1.05) * 1000));
         return result;
     }
 

src/main/java/com/rabbitmq/client/impl/ChannelManager.java

@@ -52,7 +52,7 @@ public class ChannelManager {
     private ExecutorService shutdownExecutor;
     private final ThreadFactory threadFactory;
 
-    private int channelShutdownTimeout = (int) (ConnectionFactory.DEFAULT_HEARTBEAT + ConnectionFactory.DEFAULT_HEARTBEAT * (5.0 / 100.0)) * 1000;
+    private int channelShutdownTimeout = (int) ((ConnectionFactory.DEFAULT_HEARTBEAT * 1.05) * 1000);
 
     protected final MetricsCollector metricsCollector;