MDL-28488 backup - conditionaly apply defaults based on mode

Some modes of backup cannot be preloaded with general backup
settings because they may conflict with the definitions required/set
by the mode (for example, import backups are, by definition, without
users always, so we cannot apply one default in the opposite direction).

So, after the patch, current general_backup setting will be only applied
to general backups, import/hub modes won't be using any default and
automated backup defaults should be loaded here (TODO)

backup/controller/backup_controller.class.php

@@ -339,7 +339,7 @@ class backup_controller extends backup implements loggable {
 
     protected function apply_defaults() {
         $this->log('applying plan defaults', backup::LOG_DEBUG);
-        backup_controller_dbops::apply_general_config_defaults($this);
+        backup_controller_dbops::apply_config_defaults($this);
         $this->set_status(backup::STATUS_CONFIGURED);
     }
 }