Added parameter "Show only Failed Jobs" to Unstable Jobs Portlet.

Now it's possible to have a view that shows only Failed Jobs (red) instead of Failed and Unstable Jobs (red+yellow).
Depending on your job role, it's very good to distinguish between jobs that don't worked (authentication, slaves connection, directory creating or infrastructure issues) - and jobs that worked, but just not as expected (usually XUnit test failures).


Signed-off-by: Bruno Candido Volpato da Cunha <brunocvcunha@gmail.com>