Extend integration test to include 2.1.x server series

(Status: WIP)

This patch attempts to add support for running the integration suite against a 2.1.x series of Cassandra. At the time of writing, we are using RC3. The basic strategy is to get something working in a stable fashion on Travis before merging this into the upstream. Because the logic differs slightly from the 2.0.x series, I have elected to go for a copy and paste approach to factoring the differences out. I figured that it was better to have something that works rather than some really well factored bash script, since we are not necessarily in the business of bash scripting. The logic to run the 2.0.x series is unlikely to change, so I saw a diminishing rate of return in putting too much effort into changing something that is known to work.