The init-file is not in the backup. I have built up a Galera Cluster from scratch (Ubuntu 14.04 with MariaDB 10.0). Therefore the joiner-node does not start until the init-file is created. So everything else is fine.
xtrabackup-v2 is used for SST:
The init-file lies in the the datadir (of the donor):
init-file = init-file.sql
160307 15:20:18 [ERROR] mysqld: File ‘init-file.sql’ not found (Errcode: 2 “No such file or directory”)
xtrabackup_56 version 2.1.8 for MySQL server 5.6.15 Linux (x86_64) (revision id: undefined)