As described in the inline comments, this is working around a broken
version of setuptools vendored by virtualenv currently. Specify in a
config file that it should download the latest helper tools, rather
then rely on the inbuilt versions.
Add to the base-test pre-playbook; after testing we can move to the
base playbook.
Change-Id: Ib17017637eae81a3ff57302e7c77945f2045b5ac
96052cfebf