title: jenkins git clone: can't clone to a specific directory
body: <p>According to documentation, posts and my memory, the jenkins Git plugin allows selecting the target subdirectory for a clone. I worked in another Jenkins instance I was managing.
  For some reason, in this new installation, I don't see that option. It's just not there. Git plugin is on the latest, version 2.3.1.
  I'm using the LTS release channel, so Jenkins itself is v1.580.2.</p>
  
  <p>Either I'm missing something, or something is terribly wrong with my (new) installation.</p>