permissions: allow users to update settings for repository groups they still own, or have admin perms, when they don't change their name.

- this before gave no-permission errors as the parent group access was checked
- since the group parent permission should be checked at creation, or name change this commit fixes such case

rhodecode/api/tests/test_create_repo_group.py

@@ -233,8 +233,8 @@ class TestCreateRepoGroup(object):
 
         expected = {
             'repo_group':
-                'Parent repository group `{}` does not exist'.format(
-                    repo_group_name)}
+                u"You do not have the permissions to store "
+                u"repository groups inside repository group `{}`".format(repo_group_name)}
         try:
             assert_error(id_, expected, given=response.body)
         finally: