title: Run a build step on a specific branch only
body: <p>I have a build configuration containing two build steps "Build" and "Deploy".
  This build configuration is using a Git VCS and is configured to run all branches.</p>
  
  <p>Let's assume that I currently have two branches "master" and "Feature in Development".</p>
  
  <p>I want to divide the "Deploy" step into two. "Deploy Production" and "Deploy Beta".
  The "Deploy Production" step should only be executed when the master branch was changed and is currently building.</p>
  
  <p>Is there a built in possibility to do that or do I have to check the %teamcity.build.branch.is_default% variable manually within the script?</p>