Make ClearConnectionPool test work with MySql.Data.
Make ClearConnectionPool test work with MySql.Data.

ClearPoolAsync API has a different signature in MySqlConnector.

Because all MySql.Data async methods execute synchronously, the SLEEP
commands had finished by the time SHOW FULL PROCESSLIST was executed.
Instead, use MySqlConnection.ServerThread to get the actual connection ID
of each open connection. (This should also help prevent test failures from
coincidentally having an unrelated query running when SHOW FULL
PROCESSLIST is executed.)

gitsno/MySqlConnector,gitsno/MySqlConnector,mysql-net/MySqlConnector,mysql-net/MySqlConnector