BigQuery: update system test to use test data in bigquery-public-data. (#5965)

Author: shollyman

tests/system.py

@@ -321,11 +321,11 @@ def test_get_table_w_public_dataset(self):
 
     def test_list_partitions(self):
         table_ref = DatasetReference(
-            'bigquery-partition-samples',
-            'samples').table('stackoverflow_comments')
+            'bigquery-public-data',
+            'ethereum_blockchain').table('blocks')
         all_rows = Config.CLIENT.list_partitions(table_ref)
-        self.assertIn('20150508', all_rows)
-        self.assertEquals(2066, len(all_rows))
+        self.assertIn('20180801', all_rows)
+        self.assertGreater(len(all_rows), 1000)
 
     def test_list_tables(self):
         DATASET_ID = _make_dataset_id('list_tables')