Improve reconnection settings

I've added support for maximum retries and updated the tests. Additionally, RedisSpecBase was updated to use the [Akka TestKit](http://doc.akka.io/docs/akka/2.3.0/scala/testing.html). The ExponentialReconnectionSettings have been updated and fixed (they would overflow previously).

I'd still like a test for maximum retries but I'm haven't been able to find a solution.

I look forward to your feedback.