Serializers user signup: correctly handle EtebaseValidationErrors.

Don't coerce them to strings

django_etebase/serializers.py

@@ -450,6 +450,8 @@ class AuthenticationSignupSerializer(BetterErrorsMixin, serializers.Serializer):
                 # Create the user and save the casing the user chose as the first name
                 try:
                     instance = create_user(**user_data, password=None, first_name=user_data['username'], view=view)
+                except EtebaseValidationError as e:
+                    raise e
                 except Exception as e:
                     raise EtebaseValidationError('generic', str(e))