title: Clean jenkins queue of jobs when jobs of the same branch are pending
body: <p>Our team is using merge requests to ensure code reviews.
  We use jenkins as our CI server.</p>
  
  <p>Some times while reviewing a given branch we push a lot of commits to a given branch. And in jenkins we trigger a build for each commit.</p>
  
  <p>Is there a way to clear the jenkins job queue automatically if it detects multiple jobs for the same branch? Just keeping the most recent job? to ensure the latest commit is built.</p>