automated: linux: dsdbench: only save stdout to logfile

Because of this bug https://bugs.linaro.org/show_bug.cgi?id=2694, the
error message destroys the structure of logfile, and causes parser not
working.

Change-Id: I76b7b0b71f5427da53e1778e0abc69ac2f180c17
Signed-off-by: Chase Qi <chase.qi@linaro.org>
1 file changed