rcuscale: Add laziness and kfree tests

This commit adds 2 tests to rcuscale.  The first one is a startup test
to check whether we are not too lazy or too hard working.  The second
one causes kfree_rcu() itself to use call_rcu() and checks memory
pressure. Testing indicates that the new call_rcu() keeps memory pressure
under control roughly as well as does kfree_rcu().

[ paulmck: Apply checkpatch feedback. ]

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>