torture: Add kvm-remote.sh script for distributed rcutorture test runs

This commit adds a kvm-remote.sh script that prepares a tarball that
is then downloaded to the remote system(s) and executed.  The user is
responsible for having set up the remote systems to run qemu, but all the
kernel builds are done on the system running the kvm-remote.sh script.
The user is also responsible for setting up the remote systems so that
ssh can be run non-interactively, given that ssh is used to poll the
remote systems in order to detect completion of each batch.

See the script's header comment for usage information.

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