Skip tests using performance_schema if the it is not enabled.
Skip tests using performance_schema if the it is not enabled.

Fix the test failures in client_spec.rb on MariaDB.

On MariaDB >= 10.0, the setting of the peformance schema is disabled by defult.
https://jira.mariadb.org/browse/MDEV-6726

You can comfirm the status by the SQL `SHOW VARIABLES LIKE 'performance_schema`.

jeremy/mysql2,brianmario/mysql2,sodabrew/mysql2,jeremy/mysql2,jeremy/mysql2,sodabrew/mysql2,sodabrew/mysql2,brianmario/mysql2,brianmario/mysql2