roles/samba-dc: Correct restorecon path

Evidently, some files in `/var/lib/samba` match multiple file context
rules. Thus, when running `restorecon` against the entire
`/var/lib/samba` directory, files in the `bind-dns` subdirectory may end
up with the wrong label. To work around this issue, `restorecon` is now
run only on that subdirectory to ensure the correct labels are applied.

This is likely to cause problems when a full filesystem relabel is
scheduled.

roles/samba-dc/handlers/main.yml

@@ -1,5 +1,5 @@
 - name: restore samba file contexts
-  command: restorecon -RF /var/lib/samba
+  command: restorecon -RF /var/lib/samba/bind-dns
 - name: display generated admin password
   debug:
     var=samba_dc_provision.admin_password