Make it easy to re-run failed test suite scenarios

This MR adds automatic support for saving rerun files. They are useful for #19072 (closed), and I don't see why they should be optional.

With this in place, you don't need to do anything fancy to save rerun files:

sudo ./run_test_suite --disable-chu --iso  ~/tails/isos/last.iso -- features/build.feature:7

And you can hook simple quirks to use those files again:

while true; do
    sudo ./run_test_suite --disable-chu --iso  ~/tails/isos/last.iso --  "@$(find /tmp/TailsToaster/ -maxdepth 1 -type f -name 'rerun-*.txt'  -print0 | xargs -0 ls -t1|head -n1)"
    sleep 1
done

I was tempted to encode this into some wrapper, but then I find myself wondering:

• shall I exclude empty files, so my CPU keeps getting busy? It's just | stest -s in the previous oneliner, but would require some option
• shall I include all previous failures (useful when making release)? Use the oldest file (useful when making release) or the newest one (useful when developing)

So I decided not to include such a wrapper and just see what usage we find ourselves using in the future.

Closes #19072 (closed)