Change volume client methods to return one value

Change volume client methods to return one value and update tests.

Partially implements: blueprint clients-return-one-value

Change-Id: I017b9a69f5da9c6fac0a46acae037a2a912bef97
diff --git a/tempest/api/volume/test_volumes_snapshots.py b/tempest/api/volume/test_volumes_snapshots.py
index b7e9422..179eb09 100644
--- a/tempest/api/volume/test_volumes_snapshots.py
+++ b/tempest/api/volume/test_volumes_snapshots.py
@@ -44,11 +44,11 @@
         and validates result.
         """
         if with_detail:
-            _, fetched_snap_list = \
+            fetched_snap_list = \
                 self.snapshots_client.\
                 list_snapshots_with_detail(params=params)
         else:
-            _, fetched_snap_list = \
+            fetched_snap_list = \
                 self.snapshots_client.list_snapshots(params=params)
 
         # Validating params of fetched snapshots
@@ -94,14 +94,14 @@
         snapshot = self.create_snapshot(self.volume_origin['id'], **params)
 
         # Get the snap and check for some of its details
-        _, snap_get = self.snapshots_client.get_snapshot(snapshot['id'])
+        snap_get = self.snapshots_client.get_snapshot(snapshot['id'])
         self.assertEqual(self.volume_origin['id'],
                          snap_get['volume_id'],
                          "Referred volume origin mismatch")
 
         # Compare also with the output from the list action
         tracking_data = (snapshot['id'], snapshot[self.name_field])
-        _, snaps_list = self.snapshots_client.list_snapshots()
+        snaps_list = self.snapshots_client.list_snapshots()
         snaps_data = [(f['id'], f[self.name_field]) for f in snaps_list]
         self.assertIn(tracking_data, snaps_data)
 
@@ -110,13 +110,13 @@
         new_desc = 'This is the new description of snapshot.'
         params = {self.name_field: new_s_name,
                   self.descrip_field: new_desc}
-        _, update_snapshot = \
+        update_snapshot = \
             self.snapshots_client.update_snapshot(snapshot['id'], **params)
         # Assert response body for update_snapshot method
         self.assertEqual(new_s_name, update_snapshot[self.name_field])
         self.assertEqual(new_desc, update_snapshot[self.descrip_field])
         # Assert response body for get_snapshot method
-        _, updated_snapshot = \
+        updated_snapshot = \
             self.snapshots_client.get_snapshot(snapshot['id'])
         self.assertEqual(new_s_name, updated_snapshot[self.name_field])
         self.assertEqual(new_desc, updated_snapshot[self.descrip_field])
@@ -172,7 +172,7 @@
         # create a snap based volume and deletes it
         snapshot = self.create_snapshot(self.volume_origin['id'])
         # NOTE(gfidente): size is required also when passing snapshot_id
-        _, volume = self.volumes_client.create_volume(
+        volume = self.volumes_client.create_volume(
             size=1,
             snapshot_id=snapshot['id'])
         self.volumes_client.wait_for_volume_status(volume['id'], 'available')