blocker_list: use 'Discuss' for accepted trackers
    
    Adam had a point that it's slightly confusing that even accepted blockers have
    a 'Vote' link displayed. Let's change it to 'Discuss' for accepted trackers,
    keep 'Vote!' for proposed trackers.
    
    Merges: https://pagure.io/fedora-qa/blockerbugs/pull-request/131