Make fix-products-paths more reusable.

Also, simplify syntax (no need for a loop).
Also, actually propagate error from all commands.

stack/erp5/buildout.cfg

@@ -351,8 +351,9 @@ git-executable = ${git:location}/bin/git
 [fix-products-paths]
 recipe = plone.recipe.command
 stop-on-error = true
+dir = ${erp5:location}
 command =
-  for DIR in "${erp5:location}"; do cd "$DIR"; rm -f Products ; ln -s product Products; touch product/__init__.py; done
+  rm -f "${:dir}/Products" && ln -s product "${:dir}/Products" && touch "${:dir}product/__init__.py"
 update-command = ${:command}
 
 [testrunner]