Synced xtrabackup SST scripts from PXC source tree as of PXC 5.6.27-25.13
- PXC#480: xtrabackup-v2 SST fails with multiple log_bin directives in my.cn
- PXC#460: wsrep_sst_auth don't work in Percona-XtraDB-Cluster-56-5.6.25-25.
- PXC-416: Fix SST related issues.
- PXC-389: Merge remote-tracking branch 'wsrep/5.6' into 5.6-wsrep-pxc389
- Bug #1431101: SST does not clobber backup-my.cnf