LU-7884 landed a patch that touches a file before loopback mounting it and it works for ldiskfs,
but for zfs in utils/mkfs/mount_utils_zfs.c::zfs_create_vdev() we check if the file exists and if it does not, we create it with the specified size, but since the patch here creates the file, zfs vdev attachment always fails due to existign file of less than 64M.

Need to fix this up somehow, I guess.