Do not use self.volume_origin in volume.base.attach_volume

In volume.base.attach_volume, the addCleanup uses
self.volume_origin which will make the function can't
be used elsewhere.

Change-Id: Ibe7f81700b1c668c27e48a2e4b4557dafe7f0eb7
diff --git a/tempest/api/volume/base.py b/tempest/api/volume/base.py
index 7cd72e1..9f522bd 100644
--- a/tempest/api/volume/base.py
+++ b/tempest/api/volume/base.py
@@ -181,7 +181,7 @@
         self.addCleanup(waiters.wait_for_volume_status, self.volumes_client,
                         volume_id, 'available')
         self.addCleanup(self.servers_client.detach_volume, server_id,
-                        self.volume_origin['id'])
+                        volume_id)
 
     @classmethod
     def clear_volumes(cls):