[1.8.x] Explicitly checked for LookupError in contenttypes migration

Backport of 4dd1f4c5eb from master

django/contrib/contenttypes/migrations/0002_remove_content_type_name.py

@@ -9,7 +9,7 @@ def add_legacy_name(apps, schema_editor):
     for ct in ContentType.objects.all():
         try:
             ct.name = apps.get_model(ct.app_label, ct.model)._meta.object_name
-        except:
+        except LookupError:
             ct.name = ct.model
         ct.save()