oeqa/selftest: Standardize json logging output directory
Currently sdk & sdkext will output json file to LOG_DIR, while
selftest will output json file to TOPDIR/log.
Standardize selftest json output file to LOG_DIR.
(From OE-Core rev: 2012d6b076fc833864a0254d56d78536314a6799)
Signed-off-by: Yeoh Ee Peng <ee.peng.yeoh@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>