`sudo` does not make admins escape from the sandboxes

We are using `pam_namespace`'s `unmnt_remnt` option, which should make `pam_namespace` perform a namespace switch when changing users.
Yet, `sudo`-ing to `root` doesn't make one escape the mount namespaces.

However, SSH-ing as `root` gives the expected result (no mount namespaces), so it isn't a misconfiguration on that side.
