Docker for Cayenne test databases

[Andrus Adamchik <an...@objectstyle.org>]

I think we should start using Docker to unify and streamline our cross-DB testing. Since most major DBs are already available as images on dockerhub (with notable exception of SQLServer obviously), we can create simple and reproducible recipes for each DB test. 

Now if we could also integrate this with Jenkins at Apache somehow... A slow version of that may be possible: We can run the containers on EC2, using an IP-based firewall, and use TLS JDBC connections if available. But maybe ASF infra has better ideas.

Andrus