simple client integration tests

Still need to add some sort of `@cassandra-version-specific @cassandra-version-2.0` to the C* 2.0 features. Also will need to update rake task in Rakefile/Travis to include the new integration tests suite.
you should run the at_exit hook only once per cluster initialization. something like:

```ruby
$ccm_cluster ||= begin
  cluster = CCM.setup_cluster(1, 1)
  at_exit do
    $ccm_cluster.stop
    $ccm_cluster = nil
  end
  cluster
end