Update the test file of tracker_by_command
openQA test in scenario sle-15-Installer-DVD-x86_64-desktopapps-other@64bit-virtio-vga fails in
The test file in this case is an empty file however tracker can't index empty file( I will file a bug for this).
We should replace the empty file with a text file.
Fails since (at least) Build 408.1