user_stats and testcase_stats: filter out bugs that aren't bugs
    
    We noticed today that some results have been filed with free-text
    comments in the template where bug numbers are supposed to go.
    This makes both user_stats and testcase_stats generate some bad
    output (attempting to link the free text as a Bugzilla bug ID,
    and for user_stats, just printing it off in a column that's not
    meant to be very wide, which looks awkward). This fixes that by
    filtering out any "results" which aren't actually bug numbers at
    the output generation stage.
    
    We could also change this in wikitcms so it only includes bugs
    in the Result instance if the text is really a digit, but that
    seems like a bigger gun and there may possibly be cases where we
    do want to include "bugs" that aren't RHBZ bug numbers (maybe
    like 'bgo#123' or something), so I decided to just do it here for
    now.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>