Changes

ansible/setup-jenkins: add more utils

* etckeeper: to automatically have /etc changes versioned in git; we
  already use it in various other places
* ncdu: to figure out what consumes space
* tree: list directory trees, useful to quickly check if e.g. ccache
  and jenkins workspace dirs are populated properly

Change-Id: I4b0e5a21f77d0ffb60f1f3aaf91aecd08cb2fe90