Add explicitely lxml egg installation

software/agent/software.cfg

@@ -50,12 +50,16 @@ update-command = ${:command}
 command = grep parts ${buildout:develop-eggs-directory}/slapos.toolbox.egg-link
 
 [instance-recipe]
+# XXX-Cedric: it can use newest slapos.cfg to not have duplication
 egg = slapos.cookbook
 module = agent
 
 [instance-recipe-egg]
+# XXX-Cedric: it can use newest slapos.cfg to not have duplication
 recipe = zc.recipe.egg
-eggs = ${instance-recipe:egg}
+eggs =
+  ${lxml-python:egg}
+  ${instance-recipe:egg}
 
 [template]
 recipe = slapos.recipe.template