intel/tools: Use subprocess.Popen to read output directly from a pipe

intel/tools: Use subprocess.Popen to read output directly from a pipe

Instead of using tempfiles to communicate between child & parent
process. The latter sometimes resulted in hitting the meson timeout if
there was high filesystem pressure.

Fixes: ccaa5b034f48 "intel/tools: rewrite run-test.sh in python"
Reviewed-by: Dylan Baker <dylan.c.baker@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9528>