BUG: NFSv4 fscontext mount results in an unlabeled directory

Mounting a security_label exported NFS4 filesystem with a fscontext= mount option to override the default superblock security context (not the per-file contexts) yields an unlabeled directory. Until this is fixed, we cannot fix/restore the corresponding selinux testsuite tests, see https://github.com/SELinuxProject/selinux-testsuite/issues/91