"Kubernetes is unhappy with our Docker image because we start systemd
under the hood. Fix that by switching to use "supervisord" to manage the
two processes -- "scylla" and "scylla-jmx":
http://blog.kunicki.org/blog/2016/02/12/multiple-entrypoints-in-docker/
While at it, fix up "docker logs" and "docker exec cqlsh" to work
out-of-the-box, and update our documentation to match what we have.
Further work is needed to ensure Scylla production configuration works
as expected and is documented accordingly."
(cherry picked from commit 28ee2bdbd2)
