RedundancyGroupState: change state texts to 'unreachable' or 'reachable'

The state text is only necessary to add css rules for state-balls and not be used to show the
state text of the group.

library/Icingadb/Model/RedundancyGroupState.php

@@ -65,6 +65,7 @@ class RedundancyGroupState extends Model
 
     public function getStateText(): string
     {
-        return $this->failed ? 'problem' : 'ok';
+        // The method should only be called to fake state balls and not to show the group's state
+        return $this->failed ? 'unreachable' : 'reachable';
     }
 }