title: TFS Condition pull request from specific branch
body: <p>There is any way to condition a pull request to come from an specific branch on Team Foundation Server 2017 ? 
  We are implementing <a href="http://nvie.com/posts/a-successful-git-branching-model/" rel="nofollow noreferrer">gitflow</a> and we would like to enforce pull requests to master always come from develop or hotfix branches .</p>