Fixed #20088 -- Changed get_admin_log not to depend on User id field

Before this change, the get_admin_log method would expect User model's
FK to be named `id`. When changing that FK name, admin/index.html
rendering would fail.

This includes:
 * Changed the use of id for the use of pk property.
 * Added a regression test that fails without the patch.

This commit refs #20088.

tests/admin_changelist/models.py

@@ -87,3 +87,6 @@ class OrderedObject(models.Model):
     number = models.IntegerField(default=0, db_column='number_val')
 
     objects = OrderedObjectManager()
+
+class CustomIdUser(models.Model):
+    uuid = models.AutoField(primary_key=True)