Disabled stripping of test selectors in all builds

no issue

- we want to run e2e tests against production Ghost instances and having test selectors available means much less brittle tests
- only real impact from keeping the selectors is extra file size in production builds but that is minimal (~6KB gzipped at time of commit)

ghost/admin/ember-cli-build.js

@@ -234,6 +234,9 @@ module.exports = function (defaults) {
                     })
                 ]
             }
+        },
+        'ember-test-selectors': {
+            strip: false
         }
     });