Fixes for scaling proxy and native charm

With changes in here, it can remove application while scaling in
and it can add application existed k8s proxy charm model.

Change-Id: If4fd378fdafd925fa1750ce4769506b44adc233c
Signed-off-by: aktas <emin.aktas@ulakhaberlesme.com.tr>
diff --git a/n2vc/n2vc_juju_conn.py b/n2vc/n2vc_juju_conn.py
index 6e78c47..7714d4e 100644
--- a/n2vc/n2vc_juju_conn.py
+++ b/n2vc/n2vc_juju_conn.py
@@ -543,13 +543,14 @@
 
         _, ns_id, _, _, _ = self._get_namespace_components(namespace=namespace)
         model_name = '{}-k8s'.format(ns_id)
-        cloud = cloud_name or self.k8s_cloud
-        credential = credential_name or cloud_name if cloud_name else self.k8s_cloud
-        await self.libjuju.add_model(
-            model_name,
-            cloud_name=cloud,
-            credential_name=credential
-        )
+        if not await self.libjuju.model_exists(model_name):
+            cloud = cloud_name or self.k8s_cloud
+            credential = credential_name or cloud_name if cloud_name else self.k8s_cloud
+            await self.libjuju.add_model(
+                model_name,
+                cloud_name=cloud,
+                credential_name=credential
+            )
         application_name = self._get_application_name(namespace)
 
         try:
@@ -762,7 +763,8 @@
         self.log.info("Namespace {} deleted".format(namespace))
 
     async def delete_execution_environment(
-        self, ee_id: str, db_dict: dict = None, total_timeout: float = None
+        self, ee_id: str, db_dict: dict = None, total_timeout: float = None,
+            scaling_in: bool = False
     ):
         self.log.info("Deleting execution environment ee_id={}".format(ee_id))
 
@@ -775,12 +777,20 @@
         model_name, application_name, _machine_id = self._get_ee_id_components(
             ee_id=ee_id
         )
-
-        # destroy the application
         try:
-            await self.libjuju.destroy_model(
-                model_name=model_name, total_timeout=total_timeout
-            )
+            if not scaling_in:
+                # destroy the model
+                # TODO: should this be removed?
+                await self.libjuju.destroy_model(
+                    model_name=model_name, total_timeout=total_timeout
+                )
+            else:
+                # get juju model and observer
+                controller = await self.libjuju.get_controller()
+                model = await self.libjuju.get_model(controller, model_name)
+                # destroy the application
+                await self.libjuju.destroy_application(
+                    model=model, application_name=application_name)
         except Exception as e:
             raise N2VCException(
                 message=(