Use volume_id rather than volume_name in volume extensions timeout

We're seeing "Volume None failed to reach in-use status within the
required time" because the volume_name is not set as displayName in the
response body, this is different between cinder v1 and v2, so just use
the volume_id in the TimeoutException message, like what the
volumes_client does in it's wait_for_volume_status method.

Related-Bug: #1398078

Change-Id: I24062b559f977d552789d850ea13e365b33070cd
diff --git a/tempest/services/compute/json/volumes_extensions_client.py b/tempest/services/compute/json/volumes_extensions_client.py
index 6b27f4a..b23b20b 100644
--- a/tempest/services/compute/json/volumes_extensions_client.py
+++ b/tempest/services/compute/json/volumes_extensions_client.py
@@ -92,7 +92,6 @@
     def wait_for_volume_status(self, volume_id, status):
         """Waits for a Volume to reach a given status."""
         resp, body = self.get_volume(volume_id)
-        volume_name = body['displayName']
         volume_status = body['status']
         start = int(time.time())
 
@@ -106,7 +105,7 @@
             if int(time.time()) - start >= self.build_timeout:
                 message = ('Volume %s failed to reach %s status within '
                            'the required time (%s s).' %
-                           (volume_name, status, self.build_timeout))
+                           (volume_id, status, self.build_timeout))
                 raise exceptions.TimeoutException(message)
 
     def is_resource_deleted(self, id):