Fix the remove mariadb volume failed

- when run tools/cleanup-containers mariadb, the mariadb volume remove
failed, because the "volumes_to_remove" can't catch the mariadb
volume, this patch to fix it.

- remove the unnecessary "()"

more test infomation, see http://paste.openstack.org/show/603359/

Closes-Bug: #1674207

Change-Id: I82f5922fcc84d222f74d2551a2c697bf78136a2d