Revert "Revert "Update desired virtualenv version everywhere""

Add upgrading of setuptools to prepare-node.sh. We want this
to happen everywhere, and quite honestly I'm not sure I
fully trust trying to get puppet to do it.

This reverts commit 3bc3a11244f4a4e28a4c97feec4987940d0f34cc.

Change-Id: Idf09be0e1e086e20f9e71ceb26602fea1fc62173