Add zc.buildout and slapos.libnetworkcache.

As soon as slapos.core (slapgrid) has zc.buildout in its search path it is
using this one. And thanks to pinning to SlapOS patched buildout and adding
slapos.libnetworkcache networkcache will become enabled on all software runs.

software/erp5testnode/software.cfg

@@ -86,6 +86,8 @@ dummy =
   ${slapos.cookbook-repository:location}
 eggs =
   ${lxml-python:egg}
+  zc.buildout
+  slapos.libnetworkcache
   slapos.core
   slapos.cookbook