parameters: introduce no_convert keyword argument

When set to true, the argument causes params to not convert unicode values
to the param type.

This will allow thin client to properly handle params which can be
converted from unicode to the param type only on the server, e.g. because
of a normalizer.

https://fedorahosted.org/freeipa/ticket/4739

Reviewed-By: David Kupka <dkupka@redhat.com>

ipalib/parameters.py

@@ -414,6 +414,7 @@ class Param(ReadOnly):
         ('sortorder', int, 2), # see finalize()
         ('option_group', unicode, None),
         ('cli_metavar', str, None),
+        ('no_convert', bool, False),
 
         # The 'default' kwarg gets appended in Param.__init__():
         # ('default', self.type, None),
@@ -808,18 +809,26 @@ class Param(ReadOnly):
 
         :param value: A proposed value for this parameter.
         """
+        if not self.no_convert:
+            convert = self._convert_scalar
+        else:
+            def convert(value):
+                if isinstance(value, unicode):
+                    return value
+                return self._convert_scalar(value)
+
         if _is_null(value):
             return
         if self.multivalue:
             if type(value) not in (tuple, list):
                 value = (value,)
             values = tuple(
-                self._convert_scalar(v) for v in value if not _is_null(v)
+                convert(v) for v in value if not _is_null(v)
             )
             if len(values) == 0:
                 return
             return values
-        return self._convert_scalar(value)
+        return convert(value)
 
     def _convert_scalar(self, value, index=None):
         """

pylint_plugins.py

@@ -152,6 +152,7 @@ ipa_class_members = {
         'alwaysask',
         'sortorder',
         'option_group',
+        'no_convert',
      ],
     'ipalib.parameters.Bool': [
         'truths',