BATCHEE-156 only log a warning on CNFE

There is one use case which might be ok:
If someone works with different implementations, e.g. different JPA providers
then the Exceptions might be different depending on implementations.
In that case the batch developer might want to add Exceptions from all the supported
implementations. And of course only one of them is available at runtime in that case.
The other enlisted classes will likely throw a NCFE.
diff --git a/jbatch/src/main/java/org/apache/batchee/container/impl/controller/chunk/ExceptionConfig.java b/jbatch/src/main/java/org/apache/batchee/container/impl/controller/chunk/ExceptionConfig.java
index 1e5b314..6536aa3 100644
--- a/jbatch/src/main/java/org/apache/batchee/container/impl/controller/chunk/ExceptionConfig.java
+++ b/jbatch/src/main/java/org/apache/batchee/container/impl/controller/chunk/ExceptionConfig.java
@@ -20,10 +20,14 @@
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
+import java.util.logging.Level;
+import java.util.logging.Logger;
 
 import org.apache.batchee.container.exception.BatchContainerRuntimeException;
 
 public class ExceptionConfig {
+    private final static Logger logger = Logger.getLogger(ExceptionConfig.class.getName());
+
     protected final Set<String> includes = new HashSet<String>();
     protected final Set<String> excludes = new HashSet<String>();
     private final ConcurrentMap<Class<? extends Exception>, Boolean> cache  = new ConcurrentHashMap<Class<? extends Exception>, Boolean>();
@@ -88,7 +92,7 @@
                     }
                 }
             } catch (final ClassNotFoundException cnfe) {
-                throw new BatchContainerRuntimeException("Cannot load class defined in the batch jobs XML: " + exClassName, cnfe);
+                logger.log(Level.WARNING, "Class {0} not found! Maybe there is a typo in yout skippable-exception-classes or repeatable-exception-classes?");
             } catch (final NoClassDefFoundError ncdfe) {
                 throw new BatchContainerRuntimeException("Cannot load parts of the class defined in the batch jobs XML: " + exClassName, ncdfe);
             }