Fix minor bug in configure application

Variable model was unassigned if the connection to the controller was
failing

Change-Id: I14764079f505c46ff7c9af7adec8079b43eca14e
Signed-off-by: David Garcia <david.garcia@canonical.com>
diff --git a/n2vc/libjuju.py b/n2vc/libjuju.py
index aa7afa1..5a3ddbb 100644
--- a/n2vc/libjuju.py
+++ b/n2vc/libjuju.py
@@ -953,15 +953,17 @@
         self.log.debug("Configuring application {}".format(application_name))
 
         if config:
+            controller = await self.get_controller()
+            model = None
             try:
-                controller = await self.get_controller()
                 model = await self.get_model(controller, model_name)
                 application = self._get_application(
                     model, application_name=application_name,
                 )
                 await application.set_config(config)
             finally:
-                await self.disconnect_model(model)
+                if model:
+                    await self.disconnect_model(model)
                 await self.disconnect_controller(controller)
 
     def _get_api_endpoints_db(self) -> [str]: