re6st: prepare OBS package using slapos.libnetworkcache

It's all the more important as OpenVPN tarballs can't be downloaded with
default Python user-agent.

`slapos.libnetworkcache` depends itself on `setuptools`.

/reviewed-on nexedi/slapos.package!88

obs/re6st/buildout.cfg.in

@@ -18,7 +18,7 @@ parts += chrpath python
 [python]
 recipe = zc.recipe.egg
 interpreter = ${:_buildout_section_name_}
-eggs = setuptools
+eggs = slapos.libnetworkcache
 # https://lab.nexedi.com/nexedi/slapos.buildout/merge_requests/11
 scripts = dummy