fix(instances): a clone stays on the host of the VM it was made from

With "VM Clone Auto Migrate" on, a new clone was migrated to a random
compute, whatever storage, CPU or network that host had, and a failed
migration showed as a failed clone although the clone existed.

The setting and its code are removed; migration appsettings.0015
deletes the setting. A clone can be migrated afterwards like any VM.
The README's update notes list the migration changes: the migration
address, storage pools for the disk check, and this setting.

appsettings/migrations/0015_remove_clone_instance_auto_migrate.py

@@ -0,0 +1,31 @@
+from django.db import migrations
+
+
+def remove_auto_migrate(apps, schema_editor):
+    """A clone stays on the host of the VM it was made from: the setting sent
+    it to a random host, whatever storage, CPU or network that host had."""
+    AppSettings = apps.get_model("appsettings", "AppSettings")
+    AppSettings.objects.using(schema_editor.connection.alias).filter(key="CLONE_INSTANCE_AUTO_MIGRATE").delete()
+
+
+def restore_auto_migrate(apps, schema_editor):
+    AppSettings = apps.get_model("appsettings", "AppSettings")
+    AppSettings.objects.using(schema_editor.connection.alias).get_or_create(
+        key="CLONE_INSTANCE_AUTO_MIGRATE",
+        defaults={
+            "name": "VM Clone Auto Migrate",
+            "value": "False",
+            "choices": "True,False",
+            "description": "Auto migrate instance after clone",
+        },
+    )
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("appsettings", "0014_login_lockout_settings"),
+    ]
+
+    operations = [
+        migrations.RunPython(remove_auto_migrate, restore_auto_migrate),
+    ]

appsettings/test_appsettings.py

@@ -43,3 +43,8 @@ class AppSettingsTestCase(TestCase):
         self.client.force_login(regular_user)
         response = self.client.get(reverse("appsettings"))
         self.assertEqual(response.status_code, 403)
+
+    def test_clones_are_not_migrated_automatically(self):
+        # a clone stays on the host of the VM it was made from; the setting
+        # that sent it to a random host is removed by migration 0015
+        self.assertFalse(AppSettings.objects.filter(key="CLONE_INSTANCE_AUTO_MIGRATE").exists())