fixed #1464 - change so persistence dir is only backed up if node is HA ...

...master or HA disabled; handles the case of HA autodetect selecting master hence the complexity.

also fixes some leaks in test and improves atomic file update support in FileBasedObjectStore.
(incorporates new logging from #1469)
See comments against `PersistenceObjectStore.prepareForContendedWrite` - feels like it could be simplified if something just told it explicitly to backup.