Make it possible to override how to get the log out link

src/Drupal/DrupalExtension/Manager/DrupalAuthenticationManager.php

@@ -148,7 +148,7 @@ public function loggedIn()
 
         // As a last resort, if a logout link is found, we are logged in. While not
         // perfect, this is how Drupal SimpleTests currently work as well.
-        if ($page->findLink($this->getDrupalText('log_out'))) {
+        if ($this->getLogoutLinkElement()) {
             return true;
         }
 
@@ -158,6 +158,14 @@ public function loggedIn()
         return false;
     }
 
+    /**
+     * Helper to get the log out link from the page.
+     */
+    public function getLogoutLinkElement()
+    {
+        return $this->getSession()->getPage()->findLink($this->getDrupalText('log_out'));
+    }
+
     /**
      * {@inheritdoc}
      */