We need an image containing the ptest packages for testing purposes.
This adds such an image based on sato-sdk. We did try appending this
in the autobuilder but it creates too much confusion about what is
going on, and increases build time due to lack of parallelisation.
(From OE-Core rev: 0f3ca0b4cae7d17d7b2d53cc433e87e1d148cdfb)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>