World writable /usr/lib/cloud-init/clouddir should not be left behind

# Bug report
[Work](https://github.com/canonical/cloud-init/pull/1690) was done last year to ensure that when `/tmp` and `/var/tmp` are hardend with `noexec`, cloud-init will use an alternative path under `/usr/lib/cloud-init`

However, `/usr/lib/cloud-init/clouddir` is created as world writable and left behind after cloud-init has exited.

## Steps to reproduce the problem
Run cloud-init with a `/tmp` and `/var/tmp` that are mounted with `noexec`

If possible, `/usr/lib/cloud-init/clouddir` should be created as non-world read/writable. But if that's not possible, at the least it should be removed when cloud-init exits.