MAGETWO-59785: Incorrect URLs in sitemap when generated from admin with 'Use...

MAGETWO-59785: Incorrect URLs in sitemap when generated from admin with 'Use Secure URLs in Admin' = Yes
Passing isSecure flag as an argument to the Store->getBaseUrl method to consider "Use Secure Urls on the storefront" (option in admin web configuration page) when building the baseUrl

app/code/Magento/Sitemap/Model/Sitemap.php

@@ -586,7 +586,8 @@ class Sitemap extends \Magento\Framework\Model\AbstractModel
      */
     protected function _getStoreBaseUrl($type = \Magento\Framework\UrlInterface::URL_TYPE_LINK)
     {
-        return rtrim($this->_storeManager->getStore($this->getStoreId())->getBaseUrl($type), '/') . '/';
+        $isSecure=$this->_storeManager->getStore($this->getStoreId())->isFrontUrlSecure();
+        return rtrim($this->_storeManager->getStore($this->getStoreId())->getBaseUrl($type, $isSecure), '/') . '/';
     }
 
     /**