Increase delay when after eventually consistent operations in datastore/storage

test/storage/e2e_test.dart

Index: test/storage/e2e_test.dart
diff --git a/test/storage/e2e_test.dart b/test/storage/e2e_test.dart
index f6c52ecf2eea0ecb2c89191e182fb4d7e635a8a0..fabbf48dff7b3d2b7f77c4ec33f45dd7f28f1d61 100644
--- a/test/storage/e2e_test.dart
+++ b/test/storage/e2e_test.dart
@@ -260,7 +260,11 @@ main() {
       return runE2EUnittest(() {
         runTests(storage, storage.bucket(testBucket));
       }).whenComplete(() {
-        storage.deleteBucket(testBucket);
+        // Deleting a bucket relies on eventually consistent behaviour, hence
+        // the delay in attempt to prevent test flakiness.
+        return new Future.delayed(STORAGE_LIST_DELAY, () {
+          return storage.deleteBucket(testBucket);
+        });
       });
     });
   });