test(05-04): add failing tests for attach File, Thumb, and bucket

- ThumbFilename/PartitionDirectory/File.Thumb behavior tests
- OpenBucket fail-loud and memblob tests
- Migrate empty plugin list must create system_files

lagoon/attach/app_test.go

@@ -0,0 +1,10 @@
+package attach
+
+import (
+	"git.golem15.com/golem15/summercms/backpack"
+	"git.golem15.com/golem15/summercms/compass"
+)
+
+func backpackApp(cfg *compass.Config) *backpack.App {
+	return backpack.New(cfg)
+}