When the thread executing a DDL was killed after finished its
execution but before writing the binlog event, the error code in
the binlog event could be set wrongly to ER_SERVER_SHUTDOWN or
ER_QUERY_INTERRUPTED.

This patch fixed the problem by ignoring the kill status when
constructing the event for DDL statements.

This patch also included the following changes in order to
provide the test case.

 1) modified mysqltest to support variable for connection command

 2) modified mysql-test-run.pl, add new variable MYSQL_SLAVE to
    run mysql client against the slave mysqld.