FSAL_LUSTRE: use fsal_filesystem lib to manage FSAL_LUSTRE.

/!\  THIS IS A WIP COMMIT, do not merge upstream !!!

/!\ this commit compiles, but work is to be done to handle "lustre-extract_fsid" correctly.
It should not be run by now.

Signed-off-by: Philippe DENIEL <philippe.deniel@cea.fr>