Leapp preupgrade fails if /dev/loop-control is missing.

Issue

• The following error was logged in the /var/log/leapp/leapp-preupgrade.log.

MountError: Mount operation with mode loop from /var/lib/leapp/scratch/diskimages/root_ to /var/lib/leapp/scratch/mounts/root_ failed: Command ['mount', '-o', 'loop', '/var/lib/leapp/scratch/diskimages/root_', '/var/lib/leapp/scratch/mounts/root_'] failed with exit code 32.