Merge ~adam-collard/maas:event-node-migration-donothing-2.7 into maas:2.7

[Adam Collard]

[2.7] Add migration for event.node to on_delete DO_NOTHING

Fixes LP:1862379

[Alberto Donato (ack)]

+1

review: Approve

diff --git a/src/maasserver/migrations/maasserver/0202_event_node_on_delete.py b/src/maasserver/migrations/maasserver/0202_event_node_on_delete.py
 new file mode 100644
index 0000000..1adc8c0
--- /dev/null
+++ b/src/maasserver/migrations/maasserver/0202_event_node_on_delete.py
@@ -0,0 +1,24 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.11 on 2020-02-07 15:57
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [("maasserver", "0201_merge_20191008_1426")]
+
+    operations = [
+        migrations.AlterField(
+            model_name="event",
+            name="node",
+            field=models.ForeignKey(
+                editable=False,
+                null=True,
+                on_delete=django.db.models.deletion.DO_NOTHING,
+                to="maasserver.Node",
+            ),
+        )
+    ]