torture: Add kvm-again.sh to rerun a previous torture-test

This commit adds a kvm-again.sh script that, given the results directory
of a torture-test run, re-runs that test.  This means that the kernels
need not be rebuilt, but it also is a step towards running torture tests
on remote systems.

This commit also adds a kvm-test-1-run-batch.sh script that runs one
batch out of the torture test.  The idea is to copy a results directory
tree to remote systems, then use kvm-test-1-run-batch.sh to run batches
on these systems.

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