filter Python unicode string prefix from jsonschema validation errors.

see: https://github.com/ansible/ansible-tower/issues/6417

awx/main/fields.py

@@ -385,6 +385,9 @@ class JSONSchemaField(JSONBField):
             self.schema(model_instance),
             format_checker=self.format_checker
         ).iter_errors(value):
+            # strip Python unicode markers from jsonschema validation errors
+            error.message = re.sub(r'\bu(\'|")', r'\1', error.message)
+
             if error.validator == 'pattern' and 'error' in error.schema:
                 error.message = error.schema['error'] % error.instance
             errors.append(error)