torture: Make kvm.sh "--dryrun sched" summarize number of batches

Knowing the number of batches that kvm.sh will split a run into allows
estimation of the duration of a test, give or take the number of builds.
This commit therefore adds a line of output to "--dryrun sched" that
gives the number of batches that will be run.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>