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/vars/main.yml

@@ -0,0 +1,19 @@
+samba_selinux_contexts:
+- path: /var/lib/samba/bind-dns/dns.keytab
+  setype: named_conf_t
+- path: /var/lib/samba/bind-dns/named.conf.*
+  setype: named_conf_t
+- path: /var/lib/samba/bind-dns/dns(/.*)?
+  setype: named_var_run_t
+samba_firewall:
+- dns
+- kerberos
+- 135/tcp
+- ldap
+- 389/udp
+- samba
+- kpasswd
+- ldaps
+- 3268/tcp
+- 3269/tcp
+- 49152-65535/tcp