overdue: util: fix config properties for consistency

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
server: fix TestOverdue.testOverdueStatus

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
invoice: payment: server: fix tests properties

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>
server: fix race condition in TestOverdue

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>