add force_permissive in config's method (iter_all, iter_group, find, find_first and make_dict)

rename _getattr to getattr

tiramisu/setting.py

@@ -603,7 +603,7 @@ class Settings(object):
                                              " '{0}' with requirement on: "
                                              "'{1}'").format(path, reqpath))
                 try:
-                    value = context._getattr(reqpath, force_permissive=True)
+                    value = context.getattr(reqpath, force_permissive=True)
                 except PropertiesOptionError as err:
                     if not transitive:
                         continue