Updating system test and docs for list_sinks() change.

Author: dhermes

docs/logging-usage.rst

@@ -342,8 +342,7 @@ List all sinks for a project:
 
    >>> from google.cloud import logging
    >>> client = logging.Client()
-   >>> sinks, token = client.list_sinks()
-   >>> for sink in sinks:
+   >>> for sink in client.list_sinks():  # API call(s)
    ...     print('%s: %s' % (sink.name, sink.destination))
    robots-storage: storage.googleapis.com/my-bucket-name
    robots-bq: bigquery.googleapis.com/projects/my-project/datasets/my-dataset

system_tests/logging_.py

@@ -398,12 +398,12 @@ def test_list_sinks(self):
         uri = self._init_storage_bucket()
         sink = Config.CLIENT.sink(SINK_NAME, DEFAULT_FILTER, uri)
         self.assertFalse(sink.exists())
-        before_sinks, _ = Config.CLIENT.list_sinks()
+        before_sinks = list(Config.CLIENT.list_sinks())
         before_names = set(sink.name for sink in before_sinks)
         sink.create()
         self.to_delete.append(sink)
         self.assertTrue(sink.exists())
-        after_sinks, _ = Config.CLIENT.list_sinks()
+        after_sinks = list(Config.CLIENT.list_sinks())
         after_names = set(sink.name for sink in after_sinks)
         self.assertEqual(after_names - before_names,
                          set([SINK_NAME]))