pyrocufflink: Ensure Samba security is correct

Usually, the *samba* role is deployed as a dependency of the *winbind*
role, which explicitly sets `samba_security` to `ads`. The new
*fileserver* role also depends on the *samba* role, but it does NOT sett
that variable. This can cause `smb.conf` to be rewritten with a
different value whenever one or the other role is applied.

Explicitly setting the `samba_security` variable at the group level
ensures that the value is consistent no matter how the *samba* role is
applied. Since all domain member machines need the same value,
regardless of what function they perform, this is safe.

group_vars/pyrocufflink/main.yml

@@ -1,4 +1,5 @@
 krb5_realm: PYROCUFFLINK.BLUE
+samba_security: ads
 samba_use_winbind: true
 pam_winbind: true
 nss_winbind: true