Set finagle-redis tests integration tests up to run as integration tests in SBT and Travis CI

We're currently excluding the finagle-redis integration tests in the SBT build. We should move them to the appropriate location, configure SBT to treat them as integration tests, and set up the Travis CI build to have a Redis server available to run them. (If this has a large impact on the Travis CI testing times we might need to turn them off there, but they currently run pretty quickly on my local machine.)