rcutorture: Check preemption for failing reader

rcutorture: Check preemption for failing reader

This commit checks to see if the RCU reader has been preempted within
its read-side critical section for RCU flavors supporting this notion
(currently only preemptible RCU).  If such a preemption occurred, then
this is printed at the end of the "Failure/close-call rcutorture reader
segments" list at the end of the rcutorture run.

[ paulmck: Apply kernel test robot feedback. ]

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Tested-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>