feat(logs): admin changes and logins are recorded on the Logs page

The Logs page shows who added, changed or deleted a compute, from web
or API, and every login, failed login, lockout and logout, with the
client address and a Result column (Done, Failed, Unknown for older
rows). A failed change is recorded with its reason and the error still
reaches the user; a refused one is recorded too.

- logs.audit.write saves each row in its own savepoint and never
  raises, so a log write cannot break or undo the action it records.
  The audit() context manager writes one row when the change ends.
- Logs gains success and ip; user, host and instance are wider and
  date is indexed. The page orders by date then id.
- A compute edit names the changed fields; an edit that changes
  nothing writes no row, and an empty password field is no change.
- A compute's VMs leaving the panel get a system row each: owners
  kept on the Removed VMs page, moved to another compute, restored,
  left without owners, or the removed record expired.
- Job rows carry the result. A job's log entry that cannot be
  computed is logged and skipped instead of rolling back the finish
  (test_service.py changes this on purpose).
- Logins are recorded by signal receivers; CustomLoginView is removed
  and the plain LoginView is used. A wrong OTP code is a failed login,
  counted by django-axes toward the lockout.

Panel records and host-side objects follow in the next layers.

admin/tests/test_views.py

@@ -4,11 +4,13 @@ from django.shortcuts import reverse
 from django.test import RequestFactory, TestCase
 
 from accounts.models import UserAttributes
+from logs.models import Logs
 
 
 class AdminTestCase(TestCase):
     def setUp(self):
         self.client.login(request=RequestFactory().get("/"), username="admin", password="admin")
+        Logs.objects.all().delete()  # the login's row
 
     def test_group_list(self):
         response = self.client.get(reverse("admin:group_list"))
@@ -134,3 +136,29 @@ class AdminTestCase(TestCase):
     def test_logs(self):
         response = self.client.get(reverse("admin:logs"))
         self.assertEqual(response.status_code, 200)
+
+    def test_logs_show_result_and_ip(self):
+        Logs.objects.create(message="first", success=True, ip="192.0.2.7")
+        Logs.objects.create(message="second", success=False)
+        Logs.objects.create(message="third")
+        response = self.client.get(reverse("admin:logs"))
+        self.assertContains(response, "Done")
+        self.assertContains(response, "Failed")
+        self.assertContains(response, "Unknown")
+        self.assertContains(response, "192.0.2.7")
+
+    def test_logs_order_ties_by_id(self):
+        first = Logs.objects.create(message="first")
+        second = Logs.objects.create(message="second")
+        Logs.objects.filter(id__in=[first.id, second.id]).update(date=first.date)
+        response = self.client.get(reverse("admin:logs"))
+        self.assertEqual([log.id for log in response.context["logs"]], [second.id, first.id])
+
+    def test_logs_bad_page_numbers(self):
+        Logs.objects.create(message="entry")
+        response = self.client.get(reverse("admin:logs"), {"page": "abc"})
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.context["logs"].number, 1)
+        response = self.client.get(reverse("admin:logs"), {"page": "999"})
+        self.assertEqual(response.status_code, 200)
+        self.assertEqual(response.context["logs"].number, response.context["logs"].paginator.num_pages)