MAGETWO-43599: Prepare Pull Request for Gallery Widget on Configurable Product

- CSP test
- Fix translation

Author: guz-anton

app/code/Magento/Catalog/view/frontend/templates/product/view/gallery.phtml

@@ -15,7 +15,8 @@
 <div class="gallery-placeholder _block-content-loading" data-gallery-role="gallery-placeholder">
     <div data-role="loader" class="loading-mask">
         <div class="loader">
-            <img src="<?php /* @escapeNotVerified */ echo $block->getViewFileUrl('images/loader-2.gif'); ?>" alt="Loading...">
+            <img src="<?php /* @escapeNotVerified */ echo $block->getViewFileUrl('images/loader-1.gif'); ?>"
+                 alt="<?php /* @escapeNotVerified */ echo __('Loading...') ?>">
         </div>
     </div>
 </div>