BackupStatusMgr, Flush CRON and bug fix

1. Make backup/snapshot status manager store additional details like meta file location.
2. Ensure it can save last 60 snapshot days.
3. Allow bindable values on how to save snapshot status in file/datastore. Default implementation stores in a file on the local instance.
4. Non-backward compatible. The previous backup file gets overwritten with new values(null) during the upgrade process.
5. By default flush scheduler type is HOUR (backward compatible). If the flush interval is not set, the flush task is considered OFF. Similar behavior for CRON.
6. Resource leak (Too many open files) while calling CassandraMonitor.
   Note: JVM GC should clean the file descriptors, but there could be a situation where JVM GC is not able to keep up.