GH-642: Increase test timeout

Fixes #642

spring-kafka/src/test/java/org/springframework/kafka/listener/ConcurrentMessageListenerContainerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 the original author or authors.
+ * Copyright 2016-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -587,7 +587,7 @@ private void testAckOnErrorWithManualImmediateGuts(String topic, boolean ackOnEr
 
 		// only one message should be acknowledged, because second, starting with "b"
 		// will throw RunTimeException and acknowledge() method will not invoke on it
-		for (int i = 0; i < 100; i++) {
+		for (int i = 0; i < 300; i++) {
 			if (consumer.position(new TopicPartition(topic, 0)) == 1) {
 				break;
 			}