Comment 0 for bug 1684090

http://autopkgtest.ubuntu.com/packages/livecd-rootfs

Log part from amd64:
...
+ udevadm settle
+ '[' -n /dev/mapper/loop0p1 -a -b /dev/mapper/loop0p1 ']'
+ '[' -e /etc/mtab ']'
+ apt-get -qqy install zerofree
+ e2fsck -y -E discard /dev/mapper/loop0p1
e2fsck 1.43.4 (31-Jan-2017)
cloudimg-rootfs: clean, 63584/274176 files, 284703/548091 blocks
+ zerofree /dev/mapper/loop0p1
+ rmdir mountpoint
+ clean_loops
+ '[' -n binary/boot/disk-uefi.ext4 ']'
+ kpartx -v -d binary/boot/disk-uefi.ext4
device-mapper: remove ioctl on loop0p1 failed: Device or resource busy
del devmap : loop0p15
del devmap : loop0p14
loop deleted : /dev/loop0
+ clean_loops
+ '[' -n binary/boot/disk-uefi.ext4 ']'
+ kpartx -v -d binary/boot/disk-uefi.ext4
device-mapper: remove ioctl on loop0p1 failed: Device or resource busy
loop deleted : /dev/loop0
E: config/hooks/033-disk-image-uefi.binary failed (exit non-zero). You should check for errors.
P: Begin unmounting filesystems...
...