TAMAYA-277: Fix warning

Use logger instead of dumping the stacktrace to System.err
diff --git a/code/core/src/main/java/org/apache/tamaya/core/internal/OSGIServiceLoader.java b/code/core/src/main/java/org/apache/tamaya/core/internal/OSGIServiceLoader.java
index 91367a7..48331c2 100644
--- a/code/core/src/main/java/org/apache/tamaya/core/internal/OSGIServiceLoader.java
+++ b/code/core/src/main/java/org/apache/tamaya/core/internal/OSGIServiceLoader.java
@@ -248,7 +248,7 @@
                 LOG.fine("Creating Service...:" + serviceClass.getName());
                 return serviceClass.getConstructor().newInstance();
             } catch (Exception ex) {
-                ex.printStackTrace();
+                LOG.log(Level.SEVERE, "Error while creating service.", ex);
                 throw new IllegalStateException("Failed to createObject service: " + serviceClass.getName(), ex);
             }
         }