Speed up tar creation

Limit recursion to the 3rd level to keep data folder from path like
Package/SubPackage/data

I have a *lot* of crab tasks hanging around, and it takes almost 10 minutes to create the tar file when creating a new task. Indeed, crab walk into all directories and stat all files to see if it's a folder. I have tasks with sometimes 3000 jobs, and crab spend all its time stating jobs res files...

With this change, it now takes ~10s to create the tar file!

One drawback is that it now tar only 'data' folder up to the 3rd level from src,
 * src/data
 * src/Package/data
 * src/Package/Subpackage/data

but IMO, this is the intended behavior.