Consider not deleting all tables in provided database

[gmpf]

First of all, thank you for adding the feature that supports using an existing database via config/parameters rather than the user having to edit it into the code.

At the moment, however, the mysql benchmark script deletes all existing tables in the provided database. Is this really necessary? On existing systems, this behaviour limits the scope of use to databases created specifically for the test. Can't setup and teardown just delete only the table named test rather than everything? I don't see anything in the code that creates other tables, so I'm not sure what the advantage is of having it the way it is now.