Fix spurious error msgs from live-boot about failed mounts…
.. and directories already existing
mount: mounting /dev/sr0 on /run/live/persistence/sr0 failed: No such device
mount: mounting /dev/vda on /run/live/persistence/vda failed: No such device
mkdir: can't create directory '/run/live/persistence/vda3/rw': File exists
mkdir: can't create directory '/run/live/persistence/vda3/work': File exists
c.f. https://www.google.com/search?q=%22%2Flive%2Fpersistence%2Fsr0+failed%22
Edited by Marcel Partap