MAGETWO-86005: [Backport 2.2] Update functional.suite.dist.yml to handle a custom backend name #12884

 - Merge Pull Request #12884 from scribam/magento2:2.2-mftf-backend-name
 - Merged commits:
   1. 0185572

Author: ishakhsuvarov

dev/tests/acceptance/tests/functional.suite.dist.yml

@@ -25,7 +25,7 @@ modules:
     config:
         \Magento\FunctionalTestingFramework\Module\MagentoWebDriver:
             url: "%MAGENTO_BASE_URL%"
-            backend_name: admin
+            backend_name: "%MAGENTO_BACKEND_NAME%"
             browser: 'chrome'
             window_size: maximize
             username: "%MAGENTO_ADMIN_USERNAME%"