roles/samba-dc: Deploy a Samba AD DC

The *samba-dc* role installs Samba on the managed node and configures it
as an Active Directory Domain controller. A custom module,
`samba_domain` handles the provisioning using `samba-tool domain
provision` in an idempotent way.

roles/samba-dc/handlers/main.yml

@@ -0,0 +1,7 @@
+- name: restore samba file contexts
+  command: restorecon -RF /var/lib/samba
+- name: display generated admin password
+  debug:
+    var=samba_dc_provision.admin_password
+- name: save firewalld configuration
+  command: firewall-cmd --runtime-to-permanent