kiss-chroot: fix trap

[aabacchus]

If the chroot is exited with nonzero status, kiss-chroot runs die chroot failed. Then, die runs exit 1 which causes the EXIT trap to execute. However, in this scope, "$@" is "chroot failed", so the trap evaluates $1 to be "chroot" rather than the mountpoint given to the kiss-chroot script. Then, the trap tries to unmount "chroot/dev" etc rather than the true mountpoint.

This patch uses double quotes rather than single when setting the trap, so that $1 is expanded then and the mountpoint is stored for when the trap is called.

To reproduce the bug:

# /mnt/bin/kiss-chroot /mnt
...
/ # exit 1
-> chroot failed.
-> Unmounting host paths.
umount chroot/dev/shm
umount chroot/dev/pts
umount: chroot/dev/pts: no mount point specified.
umount chroot/dev
umount: chroot/dev: no mount point specified.
umount chroot/proc
umount: chroot/proc: no mount point specified.
umount chroot/run
umount: chroot/run: no mount point specified.
umount chroot/sys/firmware/efi/efivars
umount chroot/sys
umount: chroot/sys: no mount point specified.
umount chroot/tmp
umount: chroot/tmp: no mount point specified.
umount chroot/etc/resolv.conf
umount: chroot/etc/resolv.conf: no mount point specified.