Firstly, the "destination" variable was replaced with a virtualenv in
6bb1f6046b692ee2038eafd0965bd3095d6fa787; update the documentation and
prefix the name as is now standard for variables in this repo. This
is not set anywhere so I think the prefixing is OK.
Call ensure-pip before installing, and use the virtualenv_command it
exports to create the environment for the zuul-cloner binary.
Story: #2007386
Task: #39311
Change-Id: I057191bf20ab1650a8926971dd386ce9cb1f03f5
Moves the zuul-cloner shim from the zuul repo to this repo as a
role, and templates the script to allow specifying the Zuul repo
source directory.
Change-Id: Id1609ce069cce6018b53025b1bd148ad0c36ae13