use backoff instead of retrying, add App Engine tip

datastore/cloud-client/README.rst

@@ -15,14 +15,15 @@ This directory contains samples for Google Cloud Datastore. `Google Cloud Datast
 .. _Google Cloud Datastore: https://cloud.google.com/datastore/docs
 
 
-To run the sample, you need to have `Datastore Import Export Admin` role.
 
 
 Set environment variables:
   `GOOGLE_CLOUD_PROJECT` - Google Cloud project id
   `CLOUD_STORAGE_BUCKET` - Google Cloud Storage bucket name
 
-For entities import/export you also need a `Storage Admin`, or `Storage Owner` role set in your Service Account.
+Roles to be set in your Service Account and App Engine default service account:
+  `Datastore Import Export Admin`, or `Cloud Datastore Owner`, or `Owner`
+  `Storage Admin`, or `Owner`
 
 
 Setup

datastore/cloud-client/README.rst.in

@@ -8,14 +8,14 @@ product:
     `Google Cloud Datastore`_ is a NoSQL document database built for automatic
     scaling, high performance, and ease of application development.
 
-required_role: Datastore Import Export Admin
 other_required_steps: >
     Set environment variables:
       `GOOGLE_CLOUD_PROJECT` - Google Cloud project id
       `CLOUD_STORAGE_BUCKET` - Google Cloud Storage bucket name
 
-    For entities import/export you also need a `Storage Admin`, or
-    `Storage Owner` role set in your Service Account.
+    Roles to be set in your Service Account and App Engine default service account:
+      `Datastore Import Export Admin`, or `Cloud Datastore Owner`, or `Owner`
+      `Storage Admin`, or `Owner`
 
 setup:
 - auth

datastore/cloud-client/admin_test.py

@@ -15,7 +15,7 @@
 
 import admin
 import pytest
-from retrying import retry
+import backoff
 
 
 PROJECT = os.environ["GOOGLE_CLOUD_PROJECT"]
@@ -39,7 +39,7 @@ def test_get_index(self):
     def test_list_index(self):
         assert admin.list_indexes(PROJECT)
 
-    @retry(stop_max_attempt_number=3, stop_max_delay=540000)
+    @backoff.on_exception(backoff.expo, AssertionError, max_tries=3, max_time=540000)
     def test_export_import_entities(self):
         response = admin.export_entities(PROJECT, "gs://" + BUCKET)
         assert response