stack/slapos: introduce slapos-cookbook-dependencies

section to install dependencies of slapos.cookbook using slapos libraries

software/slapos-testing/software.cfg

@@ -57,7 +57,9 @@ depends = ${slapos.core-setup:egg}
 <= setup-develop-egg
 egg = slapos.cookbook[test]
 setup = ${slapos.cookbook-repository:location}
-depends = ${slapos.core-setup:egg}
+depends =
+  ${slapos.core-setup:egg}
+  ${slapos-cookbook-dependencies:eggs}
 
 [slapos.core-setup]
 <= setup-develop-egg

stack/slapos.cfg

@@ -89,6 +89,11 @@ setup = ${slapos.cookbook-repository:location}
 # Install slapos.cookbook containing all officials recipes
 [slapos-cookbook]
 recipe = zc.recipe.egg
+eggs = slapos.cookbook
+depends = ${slapos-cookbook-dependencies:eggs}
+
+[slapos-cookbook-dependencies]
+recipe = zc.recipe.egg
 eggs =
   ${lxml-python:egg}
   ${python-cffi:egg}