Bug#515718: [general] live: failures at shutdown on USB flash drive

[Filipus Klutiero <chealer@gmail.com>]

Package: general
Version: 5.0.0
Severity: normal

When shutting down Debian Live running from a USB flash drive, one gets a 
bunch of errors on tty1:

Cleaning up ifupdown....
Unmounting temporary filesystems...umount: /live/cow: device is busy
umount: /live/cow: device is busy
umount: /live: device is busy
umount: /live: device is busy
<red>failed.</red>
Deactivating swap...done.
Unmounting local filesystems...umount2: No such file or directory
umount: /filesystem.squashfs: not found
umount2: Device or resource busy
umount: /dev/sda1 busy - remounted read-only
<red>failed.</red>
live-initramfs is resyncing snapshots and caching reboot files...

Please remove the USB flash drive and press ENTER to continue:

Apparently, Debian Live doesn't have persistence by default, so that's just 
not pretty.