Updating system test and docs for list_metrics() change.

Author: dhermes

docs/logging-usage.rst

@@ -171,7 +171,7 @@ List all metrics for a project:
 
    >>> from google.cloud import logging
    >>> client = logging.Client()
-   >>> metrics, token = client.list_metrics()
+   >>> metrics = list(client.list_metrics())
    >>> len(metrics)
    1
    >>> metric = metrics[0]

system_tests/logging_.py

@@ -267,12 +267,12 @@ def test_list_metrics(self):
         metric = Config.CLIENT.metric(
             METRIC_NAME, DEFAULT_FILTER, DEFAULT_DESCRIPTION)
         self.assertFalse(metric.exists())
-        before_metrics, _ = Config.CLIENT.list_metrics()
+        before_metrics = list(Config.CLIENT.list_metrics())
         before_names = set(metric.name for metric in before_metrics)
         metric.create()
         self.to_delete.append(metric)
         self.assertTrue(metric.exists())
-        after_metrics, _ = Config.CLIENT.list_metrics()
+        after_metrics = list(Config.CLIENT.list_metrics())
         after_names = set(metric.name for metric in after_metrics)
         self.assertEqual(after_names - before_names,
                          set([METRIC_NAME]))
@@ -304,7 +304,7 @@ def test_update_metric(self):
         metric.filter_ = NEW_FILTER
         metric.description = NEW_DESCRIPTION
         metric.update()
-        after_metrics, _ = Config.CLIENT.list_metrics()
+        after_metrics = list(Config.CLIENT.list_metrics())
         after_info = {metric.name: metric for metric in after_metrics}
         after = after_info[METRIC_NAME]
         self.assertEqual(after.filter_, NEW_FILTER)