Slave test: remove slapos stack

In order to be lighter.
slave-test: add promise to self-test.
recipes to dump partition configuration or buildout section in json files
(cherry picked from commit a467c0f0541dfb10240935f8e69ae97fcc2597cb)
jsondump recipes: return paths and update files
(cherry picked from commit 362c2f6b1f018aea00e2e1b8a9dea5d647a49aa1)
jsondump recipe: use GenericBaseRecipe.