Avoid caching Connection in ConnectionProvider

[lukaseder]

This practice has been seen a couple of times on the internet, in various sample projects, blog posts, etc. It is generally not a good idea to cache the Connection in a ConnectionProvider, as the ConnectionProvider should be stateless and threadsafe to be more generally useful, e.g. when injected via DI

For example, this user refers to your example and will probably get it wrong: https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/play-framework/tXvA76ZQsJs/BoznOslsHwAJ