Add missing argument in notify_callback

This fix is related to bug 866 and caused an exception when
the charm was not found. Nonetheless it did not fix the bug.
https://osm.etsi.org/bugzilla/show_bug.cgi?id=866

Change-Id: I641834461ac508eac131c32a4c4ef3557e192b1a
Signed-off-by: Dominik Fleischmann <dominik.fleischmann@canonical.com>
diff --git a/n2vc/vnf.py b/n2vc/vnf.py
index 3bf51fa..9441f4a 100644
--- a/n2vc/vnf.py
+++ b/n2vc/vnf.py
@@ -475,6 +475,7 @@
             self.notify_callback(
                 model_name,
                 application_name,
+                "error",
                 "failed",
                 callback,
                 *callback_args,