Update live migration test for return one value

The test_live_block_migration test is missing a return one value update.

Partially implements: blueprint clients-return-one-value

Change-Id: I95eef0fc14595908832a01c9112d76a7ba474f7d
diff --git a/tempest/api/compute/test_live_block_migration.py b/tempest/api/compute/test_live_block_migration.py
index e04439f..180dffd 100644
--- a/tempest/api/compute/test_live_block_migration.py
+++ b/tempest/api/compute/test_live_block_migration.py
@@ -115,8 +115,7 @@
         actual_host = self._get_host_for_server(server_id)
         target_host = self._get_host_other_than(actual_host)
 
-        resp, volume = self.volumes_client.create_volume(1,
-                                                         display_name='test')
+        volume = self.volumes_client.create_volume(1, display_name='test')
 
         self.volumes_client.wait_for_volume_status(volume['id'],
                                                    'available')