Increase timeout for PollingConsumerEndpointTests

https://build.spring.io/browse/INT-SI50X-20

Looks like 5 seconds is not enough to wait for the test completion,
especially on CI server

* Refactor `PollingConsumerEndpointTests` to use `OnlyOnceTrigger`
from the test-support module instead of local `Trigger` implementation
* Increase timeout for latch in the `OnlyOnceTrigger` to 10 seconds

**Cherry-pick to 5.0.x**

(cherry picked from commit a65d05c)

spring-integration-test-support/src/main/java/org/springframework/integration/test/util/OnlyOnceTrigger.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -28,6 +28,8 @@ import org.springframework.scheduling.TriggerContext;
  *
  * @author Gunnar Hillert
  * @author Gary Russell
+ * @author Artem Bilan
+ *
  * @since 2.2
  *
  */
@@ -47,7 +49,6 @@ public class OnlyOnceTrigger implements Trigger {
 
 	@Override
 	public Date nextExecutionTime(TriggerContext triggerContext) {
-
 		if (this.hasRun.getAndSet(true)) {
 			this.latch.countDown();
 			return null;
@@ -95,7 +96,7 @@ public class OnlyOnceTrigger implements Trigger {
 
 	public void await() {
 		try {
-			if (!this.latch.await(5000, TimeUnit.MILLISECONDS)) {
+			if (!this.latch.await(10000, TimeUnit.MILLISECONDS)) {
 				throw new RuntimeException("test latch.await() did not count down");
 			}
 		}