torture: Add --dryrun batches to help schedule a distributed run

When all of the remote systems have the same number of CPUs, one
approach is to use one "--buildonly" run and one "--dryrun sched" run,
and then distributing the batches out one per remote system.  However,
the output of "--dryrun sched" is not made for parsing, so this commit
adds a "--dryrun batches" that provides the same information in easily
parsed form.

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