[OPENJPA-2834] also cache properties in the em - even if less useful, but no need to recompute it again and again

openjpa-persistence/src/main/java/org/apache/openjpa/persistence/EntityManagerImpl.java

@@ -1965,6 +1965,7 @@ public class EntityManagerImpl
                 props.put(userKey.equals(kernelKey) ? s : userKey, JPAProperties.convertToUserValue(userKey, kvalue));
             }
         }
+        properties = props; // no need to synchronize, we don't care of the actual ref, we just want it as value
         return props;
     }