open the OSGi service tracker, or else nothing happens...

Change-Id: I5b278f4ef72849f2910b2b58dfa9b622cc9631bd

java/com.sap.sse.security/src/com/sap/sse/security/PreferenceObjectBasedNotificationSet.java

@@ -80,6 +80,7 @@ public abstract class PreferenceObjectBasedNotificationSet<PrefT, T> implements
             this.tracker = null;
         } else {
             this.tracker = new ServiceTracker<UserStore, UserStore>(context, UserStore.class, new Cutomizer());
+            this.tracker.open();
         }
         this.lock = new NamedReentrantReadWriteLock(getClass().getName()+" for "+key, /* fair */ false);
     }