MCNAME isn't defined outside our mcextend ptest images so use a wildcard in
TESTIMAGE_FAILED_QA_ARTIFACTS instead. This unbreaks the value in other images.
(From OE-Core rev: e7af85a7b7b966685a9eeaba11628dc10c1ea44b)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>