Extend one of the sstate tests to also ensure that changing SDKMACHINE doesn't
change the target task checksums.
Also fix a typo and improve debugging by turning the diff filtering off
in all cases (if the test fails, we want to full list).
(From OE-Core rev: 24bb41f273148db023721804b98676a92f9a5f9c)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>