title: jenkins multibranch pipeline disable auto node checkout
body: <p>Currently declarative pipeline will do <code>checkout scm</code> automatically when hitting first stage.<br>
  What I want is to checkout scm within subdirectory only. (so it won't checkout same thing in root directory)  </p>
  
  <p>Since it needs jenkinsfile it already checkout once. Plus directory &amp; subdirectory I checkout thrice total...
  Is it possible to disable auto checkout in multibranch pipeline using declarative syntax?</p>