dashboard, vm: implement remove_disk on InstanceTemplate and use it instead of…

dashboard, vm: implement remove_disk on InstanceTemplate and use it instead of dispatching on appliance type

circle/dashboard/views.py

@@ -2160,10 +2160,7 @@ class DiskRemoveView(DeleteView):
         disk = self.get_object()
         app = disk.get_appliance()
 
-        if isinstance(app, Instance):
         app.remove_disk(disk=disk, user=request.user)
-        else:  # isinstance(app, InstanceTemplate)
-            app.disks.remove(disk)
         disk.destroy()
 
         next_url = request.POST.get("next")

circle/vm/models/instance.py

@@ -165,6 +165,9 @@ class InstanceTemplate(AclBase, VirtualMachineDescModel, TimeStampedModel):
     def get_absolute_url(self):
         return ('dashboard.views.template-detail', None, {'pk': self.pk})
 
+    def remove_disk(self, disk, **kwargs):
+        self.disks.remove(disk)
+
 
 class Instance(AclBase, VirtualMachineDescModel, StatusModel, OperatedMixin,
                TimeStampedModel):