selftests: net: py: color the basics in the output

selftests: net: py: color the basics in the output

Sometimes it's hard to spot the ok / not ok lines in the output.
This is especially true for the GRO tests which retries a lot
so there's a wall of non-fatal output printed.

Try to color the crucial lines green / red / yellow when running
in a terminal.

Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Acked-by: Joe Damato <joe@dama.to>
Link: https://patch.msgid.link/20260402215444.1589893-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>