staging/lustre: change Lustre URLs and mailing list

Now that the lustre.org domain has been liberated we can again
use that for the main website URL and mailing list.

Also update the URL for userspace tools downloads and Git repo.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>