Refactor the o.s.d.g.listener.StubErrorHandler class.

Implement java.lang.Iterable.

Resolves spring-projectsgh-296.

spring-data-geode/src/test/java/org/springframework/data/gemfire/listener/StubErrorHandler.java

@@ -16,20 +16,30 @@
 package org.springframework.data.gemfire.listener;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
 import java.util.List;
 
 import org.springframework.util.ErrorHandler;
 
 /**
+ * Spring {@link ErrorHandler} for testing.
+ *
  * @author Costin Leau
+ * @author John Blum
+ * @see org.springframework.util.ErrorHandler
  */
-public class StubErrorHandler implements ErrorHandler {
-
-	public List<Throwable> throwables = new ArrayList<Throwable>();
+public class StubErrorHandler implements ErrorHandler, Iterable<Throwable> {
 
+	public final List<Throwable> throwables = new ArrayList<>();
 
-	public void handleError(Throwable t) {
-		throwables.add(t);
+	@Override
+	public void handleError(Throwable throwable) {
+		this.throwables.add(throwable);
 	}
 
+	@Override
+	public Iterator<Throwable> iterator() {
+		return Collections.unmodifiableList(this.throwables).iterator();
+	}
 }