MDL-65218 recycle bin: immunize recycle bin from backup_auto_storage
As far as recycle bin is using MODE_AUTOMATED, it observes the backup_auto_storage
setting (storing backups @ real location. For recycle bin we want to ensure that
backup files are always stored in Moodle file area. In order to achieve that, we
hack the setting here via $CFG->forced_plugin_settings, so it won't interfere other
operations. See MDL-65218 for more information.
This hack will be removed once recycle bin switches to use its own backup mode, with
own preferences and 100% appart from MODLE_AUTOMATED.