Variable wsrep_slave_fk_checks actually is wsrep_slave_FK_checks

The variable wsrep_slave_fk_check as documented here: https://mariadb.com/kb/en/mariadb/galera-cluster-system-variables/#wsrep_slave_fk_checks is actually called wsrep_slave_FK_checks. It is odd that this is the only variable, at least that I can think of, that is upper case. This took me quite a while to figure out.