MAGETWO-61549: Use default URL Key

Author: Oleksandr Iegorov

app/code/Magento/CatalogUrlRewrite/Observer/CategoryUrlPathAutogeneratorObserver.php

@@ -48,7 +48,9 @@ public function execute(\Magento\Framework\Event\Observer $observer)
     {
         /** @var Category $category */
         $category = $observer->getEvent()->getCategory();
-        if ($category->getUrlKey() !== false) {
+        $useDefaultAttribute = !$category->isObjectNew() && !empty($category->getData('use_default')['url_key'])
+            && (int)$category->getData('use_default')['url_key'] === 1;
+        if ($category->getUrlKey() !== false && !$useDefaultAttribute) {
             $resultUrlKey = $this->categoryUrlPathGenerator->getUrlKey($category);
             if (empty($resultUrlKey)) {
                 throw new \Magento\Framework\Exception\LocalizedException(__('Invalid URL key'));