Q_IF not implemented (if statements in the test files)

[mjonss]

There are references to if statements (Q_IF) in the code, but it is not implemented.

In MySQL's mysql-test-run / mysqltest binary some control statements are supported like if and while: https://dev.mysql.com/doc/dev/mysql-server/latest/PAGE_MYSQL_TEST_FLOW_CONTROL.html

It would be nice if they were supported by mysql-tester as well.