Explicite define innodb_log_file_size in mysql configuration.

As described here
http://www.percona.com/forums/questions-discussions/percona-xtrabackup/17446-got-ib_logfile0-is-of-different-size-when-doing-stream-backup
xtrabackup used by percona State Snapshot Transfer during controller
initialization in HA environment has compiled default value for
innodb_log_file_size, and if it different then mysql server value,
process end with error. Defining this explicite in mysql configuration to the
same value as xtrabackup has should resolve problem.