rcutorture: Dump reader protection sequence if failures or close calls

rcutorture: Dump reader protection sequence if failures or close calls

Now that RCU can have readers with multiple segments, it is quite
possible that a specific sequence of reader segments might result in
an rcutorture failure (reader spans a full grace period as detected
by one of the grace-period primitives) or an rcutorture close call
(reader potentially spans a full grace period based on reading out
the RCU implementation's grace-period counter, but with no ordering).
In such cases, it would clearly ease debugging if the offending specific
sequence was known.  For the first reader encountering a failure or a
close call, this commit therefore dumps out the segments, delay durations,
and whether or not the reader was preempted.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Mark variables static, as suggested by kbuild test robot. ]