Update test plugin to use config file

Fixes issue 3514

Change-Id: Icdd54096fbb1b06b43f6bf3021ee2f339a96288a
Reviewed-on: http://gerrit.dmdirc.com/554
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>
Automatic-Compile: Gregory Holmes <greboid@dmdirc.com>
Reviewed-by: Gregory Holmes <greboid@dmdirc.com>