[change] Refactored Templates.get_context

Context of templates for VPN will now contain variables defined by
the related VPN server

openwisp_controller/config/base/template.py

@@ -182,16 +182,19 @@ def get_context(self, system=False):
         context = {}
         if self.default_values and not system:
             context = copy(self.default_values)
+        context.update(self.get_vpn_server_context())
         context.update(super().get_context())
         return context
 
     def get_system_context(self):
         system_context = self.get_context(system=True)
+        return OrderedDict(sorted(system_context.items()))
+
+    def get_vpn_server_context(self):
         try:
-            system_context.update(self.vpn.get_vpn_server_context())
+            return self.vpn.get_vpn_server_context()
         except (ObjectDoesNotExist, AttributeError):
-            pass
-        return OrderedDict(sorted(system_context.items()))
+            return {}
 
     def clone(self, user):
         clone = copy(self)

openwisp_controller/config/tests/test_template.py

@@ -357,7 +357,7 @@ def test_context_regression(self):
             template_qs = Template.objects.filter(type='vpn')
             self.assertEqual(template_qs.count(), 1)
             t = template_qs.first()
-            self.assertEqual(t.get_context(), _original_context)
+            self.assertDictContainsSubset(_original_context, t.get_context())
             self.assertEqual(app_settings.CONTEXT, _original_context)
 
         with self.subTest(