tests: adjust cleanup_ handler to work with init.sh

tests: adjust cleanup_ handler to work with init.sh

* tests/init.cfg (cleanup_, cleanup_fn_, cleanup_final_): Define.
* tests/t-local.sh (cleanup_final_): Use this to ensure that we
always release the lock and run rmmod.  Overriding the trap did not
do the job.
* libparted/tests/t2100-zerolen.sh: Use cleanup_fn_, not cleanup_.
* tests/t1100-busy-label.sh: Likewise.
* tests/t1101-busy-partition.sh: Likewise.
* tests/t4100-dvh-partition-limits.sh: Likewise.
* tests/t4100-msdos-partition-limits.sh: Likewise.
* tests/t6000-dm.sh: Likewise.
* tests/t8000-loop.sh: Likewise.