refperf: Output per-experiment data points

Currently, it is necessary to manually edit the console output to see
anything more than statistics, and sometimes the statistics can indicate
outliers that need more investigation.  This commit therefore dumps out
the per-experiment measurements, sorted in ascending order, just before
dumping out the statistics.

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