zc.buildout version up to 2.5.2+slapos012
 slapos.recipe.template version up to 4.3
 slapos.core version up to 1.4.4

Environment of user running `slapos node instance` should not influence the
instance.

In gunicorn v19.6 and v19.5, a bug was introduced which deletes socket when nginx worker exits.
In our case, it crashes the slaprunner and prevents it from restarting by slapos.
Let's stick to v19.4.5 until this issue is closed : https://github.com/benoitc/gunicorn/issues/1298