remove create_home_folder() & ensure_home_folder()
now: on_user_created() and on_user_login both() call provision_if_needed()
which calls **create_personal_drive_atomic()**
add a helper to find Personal drive for a user and also it's root directorry
now Drive is purely a metadata
each drive has always a root folder
this model minimize Oxicloud changes, and simplify
the Drive name is simply the folder's root's name
note: owner of Drive has more permission that an owner of the root folder
Edouard Vanbelle