MAGETWO-98132: Rename LESS var names

- fix tests

Author: omiroshnichenko

app/design/adminhtml/Magento/backend/Magento_Staging/web/css/source/module/_staging-preview.less

@@ -1,5 +1,5 @@
 // /**
-//  * Copyright © 2015 Magento. All rights reserved.
+//  * Copyright © Magento, Inc. All rights reserved.
 //  * See COPYING.txt for license details.
 //  */
 

app/design/adminhtml/Magento/backend/web/css/source/forms/_temp.less

@@ -408,6 +408,9 @@ label.mage-error {
             width: 16px;
             z-index: 1;
 
+            /**
+             * @codingStandardsIgnoreStart
+             */
             &:before {
                 &:extend(.admin__control-checkbox + label:before);
                 left: 0;
@@ -434,6 +437,7 @@ label.mage-error {
                 &:before {
                     &:extend(.admin__control-checkbox:checked + label:before);
                 }
+                //  @codingStandardsIgnoreEnd
             }
 
             &._indeterminate {