Making Cron scheduler clusterable

CronScheduler service is mostly for two service, one is RuntimeDataCleanup (http://ode.apache.org/instance-data-cleanup.html), the other one is SystemSchedulesConfig ( I am not sure if we use this feature or not, as I found it was called from DeploymentPoller.java). The CronScheduler used java.util.Timer to register TimerTask, it means that if a node crashes, this TimerTask would lost also. In order to make it clusterable, we need to make this Task persistable. So that if Node1 crashes, Node2 can pick up this task from database and run it appropriately.