Feanil/optional datadog

@jzoldak @benpatterson 

I moved around the datadog dependency because I don't need it for the admin jenkins we use in devops and so I wanted it to be optional.  I also updated the jenkins_master.yml play you're using to indicate that it is being used by testeng.
This is still the testeng master, right? If so, let's keep the word master in there too.