docker-harness got a mini-makeover

Just pushed a pretty significant update to docker-harness. It was a tool I created originally to power some of my Docker containerized database tests. I pulled out the dependencies for each database to modularize it a bit. Each database module (MySQL, PostgreSQL, Redis, Memcached) now has its own go.mod and go.sum, which means you only pull in the dependencies for the databases you actually need.…