This only impacts testing.
Note that
VersionConflict: (zc.recipe.testrunner 2.0.0 (/Users/reinout/.buildout/eggs/zc.recipe.testrunner-2.0.0-py2.7.egg), Requirement.parse('zc.recipe.testrunner==1.3.0'))
means you have to remove .installed.cfg. Pinning a recipe version in a 'recipe=' line isn't handy.