Make example spec pass again

I've found that the example spec did not pass and had to fix a few things:

 * Rake was missing from Gemfile. There was no Rakefile but something was assuming rake is functional.
 * Example group was using the wrong method from the integration example group DSL
 * Cloning CCNG the first time may take a while and it's not obvious that it's done the first time specs are executed. So I've added a hint.

CLA note: I work for Pivotal on the RabbitMQ team and was told submitting the CLA is not necessary in my case.