[recipes.py] move run arg parsing to its module.

recipe_modules/path/example.py

Index: recipe_modules/path/example.py
diff --git a/recipe_modules/path/example.py b/recipe_modules/path/example.py
index 213b07ec40f14fa3cc5ddc3942ab8492378279ac..1a175734134028b301be8e4e2f4187779dbac45f 100644
--- a/recipe_modules/path/example.py
+++ b/recipe_modules/path/example.py
@@ -67,7 +67,7 @@ def RunSteps(api):
   for p in paths_to_convert:
     after = api.path.abs_to_path(str(p))
     api.step('converted path %s' % p, ['echo', after])
-    assert after == p, p
+    assert after == p, (after, p)
 
   try:
     api.path.abs_to_path('non/../absolute')