Enabled SSL support in 'nginx'

- by default SSL support is enabled in all nginx servers if private key
  for hosts' FQDN domain is found in '/srv/pki' (see 'pki' role for
  details);

- you can disable SSL support selectively for a server, or disable
  listening on port 80 for a server;

- you can select SSL certificates either directly, or by providing
  a type (normal "certs", "combined" or "selfsigned") and optionally
  domain name (if it's not provided, default FQDN domain is used);