Fix of grow_bonzais to work with the new pnfs infrastructure

Since a few days, it's impossible to write on /pnfs from any UI.

This caused the grow_bonzais code to crash when producing catalogs: we wrote them directly on /pnfs, which is not possible anymore.

The fix that I propose here writes first the catalogs locally, then sends them (with gfal) to /pnfs.

It's intented to be a hotfix (the code is broken without it). Please check that it does indeed work for what you want to do (I did only a few check).

In particular, notice that it's very possible that the baobab code is also bugged for the same reason. If it's the case, I'll make a fix later.

EDIT: seems that the CI is broken again (cannot connect to the server). I can ensure you that everything compiles, so this can still be merged.