resolved: create stub-resolv.conf symlink with correct security label

Use symlink_atomic_label() instead of symlink_atomic() as the symlink
may need a different label than the parent directory.

Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
(cherry picked from commit 7b87bece)
(cherry picked from commit 029331f56a1b6e4fb2823a56a108f741a576d7af)