title: CircleCI: Can sections or phases of the build test deploy process be conditional
body: <p>I currently have a circle.yml with build, test and deploy sections.  I would like to parameterize the build to run nightly automation similar to this link <a href="https://circleci.com/docs/1.0/nightly-builds/" rel="nofollow noreferrer">https://circleci.com/docs/1.0/nightly-builds/</a></p>
  
  <p>When running nightly automation I would like to avoid running the deploy section all together.  Is this possible?</p>