Fix blacklisting for devices that contain the live rootfs for persistence.
what_is_mounted_on was called with "d" and not the variable ${d}. This causes that no devices are actually added to the blacklist.
We also add "/run/live/medium" as possible directory where a rootfs can be mounted. This prohibits that "/run/live/medium" is moved to "/run/live/persistence/$something" when persistence is used.
Closes: #934701