test.utils.makeRecipe: support running from software folder

Now that we also run slapos.cookbook tests from SLAPOS-SR-TEST we cannot
simply examine buildout.cfg, because unlike SLAPOS-EGG-TEST this
repository is now checked out in parts of the software folder, not the
instance folder.
So that trick of looking up the egg directories in buildout does not
work, because this is a software buildout.cfg ... instead, we assume
that the standard eggs and develop-eggs directories are used.