tests: paint known breakages in yellow

tests: paint known breakages in yellow

Yellow seems a more appropriate color than bold green when
considering the universal traffic lights coloring scheme, where
green conveys the impression that everything's OK, and amber that
something's not quite right.

Likewise, change the color of the summarized total number of known
breakages from bold red to the same yellow to be less alarmist and
more consistent with the above.

An earlier version of this patch used bold yellow but because these
are all long-known failures, reminding them to developers in bold
over and over does not help encouraging them to take a look at them
very much.  This iteration paints them in plain yellow instead to
make them less distracting.

Signed-off-by: Adam Spiers <git@adamspiers.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>