YARN-8448 attempted to fix the test-container-executor C test to be able to run as root. The test claims that it should be possible to run as root; in fact, there are some tests that only run if you use root.
One of the fixes was to change the permissions of the test's config dir to 0777 from 0755. The problem was that the directory was owned by root, but then other users would need to write files/directories under it, which would fail with 0755.
YARN-8448 fixed this by making it 0777. However, this breaks running cetest because it expects the directory to be 0755, and it's run afterwards.
The proper fix for all this is to leave the directory at 0755, but to make sure it's owned by the "nodemanager" user. Confusingly, in test-container-executor, that appears to be the username and not the yarn_username (i.e. username is the user running the NM while yarn_username is just some user running a Yarn app).