Be more resilient when querying bugzilla for open bugs
    
    Sometime we fail to retrieve the list of bugs for a component because of
    some hick ups with bugzilla.
    With this commit, we'll try up to 5 times and wait 20 seconds before
    each attempts.
    If that still fails, then too bad.
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>