The following FLUSH commands are now executed under total
order isolation:
* FLUSH DES_KEY_FILE
* FLUSH HOSTS
* FLUSH PRIVILEGES
* FLUSH QUERY CACHE
* FLUSH STATUS
* FLUSH USER_RESOURCES

This patch was backported from mysql-wsrep/5.6 commit
cdea608d9a27701d76d0deec49976aa0a08b1a56