add setuptools to dev images

[willholley]

Overview

Fixes the dev containers which were missing setuptools (perhaps lots in the transition to python 3).

Testing recommendations

docker build -t couchdb:dev dev
docker build -t couchdb:dev-cluster dev-cluster

Checklist

• Code is written and works correctly;
• Changes are covered by tests;
• Documentation reflects the changes;

[wohali]

Thanks!!