Fix broken datastore test_cursor_paging. (GoogleCloudPlatform#1457)

When there are only 6 entities being retrieved, and the page size is 5,
then the second page will not have a next cursor because all entities
have been retrieved.

Also, ignore *sponge_log.xml which are test log files.

Author: SurferJeffAtGoogle

.gitignore

@@ -20,4 +20,5 @@ secrets.tar
 junit.xml
 credentials.dat
 .nox
-.vscode/
+.vscode/
+*sponge_log.xml

datastore/cloud-client/snippets_test.py

@@ -147,7 +147,6 @@ def _():
             assert len(page_one) == 5
             assert len(page_two)
             assert cursor_one
-            assert cursor_two
 
     @eventually_consistent.mark
     def test_property_filter(self, client):