POO#29637 Replace script_output(foo) with other code

[SeroSun]

This is one of fix for poo#29637, it will influence userspace/kernel tests in QA:Head(start with qa_test_), and reduce test fail by unexpected words catching.

• Related ticket: https://progress.opensuse.org/issues/29637
• Verification run: http://10.67.133.102/tests/460
  (Test failed, but test script runs OK, especially the code change part. Log upload successful)

[okurz]

Just a minor tidy needed, rest looks like a good idea:

-        my $tarball  = "/tmp/testlog.tar.bz2";
+        my $tarball = "/tmp/testlog.tar.bz2";

[SeroSun]

@okurz thank you for reviewing, tidy fixed.