Added caching of system node information

Applied optimization found in 2.8 for caching of system node information

src/Provider/Node/SystemNodeProvider.php

@@ -8,7 +8,12 @@ class SystemNodeProvider implements NodeProviderInterface
 {
     public function getNode()
     {
-        $node = null;
+        static $node = null;
+        
+        if($node !== null) {
+            return $node;
+        }        
+        
         $pattern = '/[^:]([0-9A-Fa-f]{2}([:-])[0-9A-Fa-f]{2}(\2[0-9A-Fa-f]{2}){4})[^:]/';
         $matches = array();