make the mysql config option "innodb_log_group_home_dir" an available attribute.

"Xtrabackup-v2 SST is currently recommended if you have innodb-log-group_home-dir/innodb-data-home-dir in your cnf." --- according to http://www.percona.com/doc/percona-xtradb-cluster/5.5/wsrep-system-index.html#wsrep_sst_auth

Tested on Ubuntu 12.04, Percona XtraDB Cluster 5.6, wsrep_sst_method = xtrabackup-v2 .