rcutorture: Abstract torture-test cleanup

This commit creates a torture_cleanup() that handles the generic
cleanup actions local to kernel/torture.c.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --cc include/linux/torture.h
Simple merge

diff --cc kernel/rcu/rcutorture.c
Simple merge

diff --cc kernel/torture.c
Simple merge