Fix bug 1049: Raise exception if model does not exist when destroying a model

Change-Id: I7bc64f296d6cff695511be77a5445241a1175d8a
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/n2vc/n2vc_juju_conn.py b/n2vc/n2vc_juju_conn.py
index dbd904c..0485e69 100644
--- a/n2vc/n2vc_juju_conn.py
+++ b/n2vc/n2vc_juju_conn.py
@@ -1288,6 +1288,12 @@
             total_timeout = 3600
 
         model = await self._juju_get_model(model_name=model_name)
+
+        if not model:
+            raise N2VCException(
+                message="Model {} does not exist".format(model_name)
+            )
+
         uuid = model.info.uuid
 
         # destroy applications