automated/linux/gst-validate: Don't use tee only redirect output

Lava-dispatcher slows the execution when is too many output ([1] vs [2])
in the stdout so only redirect to a file in order to speed-up, same in
piglit related to rev 36daa3ece5.

[1] https://validation.linaro.org/scheduler/job/1776006
[2] https://validation.linaro.org/scheduler/job/1794400

Change-Id: I8aa0d43b43362765946f9e4b2c89a507ea223e69
Signed-off-by: Aníbal Limón <anibal.limon@linaro.org>
1 file changed