Comment 2 for bug 1228304

For copying the binlog files (currently only last file is
copied):

a) Can be done in xtrabackup but this requires changes to
innobackupex.

b) Otherwise, needs to be done in wsrep_sst_xtrabackup, but since
only 2 stages of copying are done, this is not possible
currently, will require potentially invasive changes here.

There is another way,

xtrabackup_binlog_info contains gtid info, if this info
can be used directly in wsrep_sst_xtrabackup and in
sst_joiner_thread