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.
Merge pull request #4 from michalskalski/master

Explicite define innodb_log_file_size in mysql configuration.