Tails Cloner is too slow

It takes way longer to clone from Tails Cloner than from Gnome Disks. This makes testing everything related to the cloning process obnoxious, as it is slow even on a VM with nvme SSD virtual USB sticks.

This is because HUGE quantities of sleep were added to the code to make it somewhat more robust against unsolved race conditions. A more resilient approach to that problem was just merged so now we can speed it up massively by reducing the sleep.