Package testmysql gives tests an admin connection to a MySQL 8 server from the DSN in
AICODED_TEST_MYSQL_DSN. Without it a test is skipped, or fails when AICODED_E2E_MYSQL is
"required". Nothing here prints the DSN, which holds a password.
User creates a database and a user identified with plugin that may use only that database,
drops both when the test ends, and returns them with the user's password. The account's host
is '%', since a server in Docker sees clients at the bridge address.