Handle NoClassDefFoundError consistently for TELs

Prior to this commit, a NoClassDefFoundError caught in
TestContextManager's retrieveTestExecutionListeners() method would be
handled differently for implicit default listeners (i.e., listeners not
declared via @TestExecutionListeners) and listeners explicitly declared
via @TestExecutionListeners. Specifically, a NoClassDefFoundError would
cause a test to fail for an explicitly declared TestExecutionListener
but not for an implicitly declared one.

This commit addresses this issue by:

 - Always swallowing a NoClassDefFoundError for both implicitly and
   explicitly declared TestExecutionListeners.
 - Changing the log level from DEBUG to INFO to make such situations
   more visible to the average end user.

Issue: SPR-11347

spring-test/src/main/java/org/springframework/test/context/TestContextManager.java

@@ -180,7 +180,6 @@ public class TestContextManager {
 		List<Class<? extends TestExecutionListener>> classesList = new ArrayList<Class<? extends TestExecutionListener>>();
 
 		AnnotationDescriptor<TestExecutionListeners> descriptor = findAnnotationDescriptor(clazz, annotationType);
-		boolean defaultListeners = false;
 
 		// Use defaults?
 		if (descriptor == null) {
@@ -188,7 +187,6 @@ public class TestContextManager {
 				logger.debug("@TestExecutionListeners is not present for class [" + clazz + "]: using defaults.");
 			}
 			classesList.addAll(getDefaultTestExecutionListenerClasses());
-			defaultListeners = true;
 		}
 		else {
 			// Traverse the class hierarchy...
@@ -232,15 +230,10 @@ public class TestContextManager {
 				listeners.add(BeanUtils.instantiateClass(listenerClass));
 			}
 			catch (NoClassDefFoundError err) {
-				if (defaultListeners) {
-					if (logger.isDebugEnabled()) {
-						logger.debug("Could not instantiate default TestExecutionListener class ["
-								+ listenerClass.getName()
-								+ "]. Specify custom listener classes or make the default listener classes available.");
-					}
-				}
-				else {
-					throw err;
+				if (logger.isInfoEnabled()) {
+					logger.info(String.format("Could not instantiate TestExecutionListener class [%s]. "
+							+ "Specify custom listener classes or make the default listener classes "
+							+ "(and their dependencies) available.", listenerClass.getName()));
 				}
 			}
 		}