Make the test runner more stable with 'safe' options

More adjustments to make migration tests to behave nicely with all the 'safest' options that can be used on the test runner to ensure environmental stability, in other words, how each test can influence the result of the other.

Oh, by the way, by 'safest' options, we currently specifically mean:

    ./run -t qemu --restart-vm  --restore-image --restore-image-between-tests