Added support for dns_alt_names.

Added support for adding additional SubjectAltNames when defining a puppet master. Unless specified, it will still use "puppet" in addition to the FQDN.

As an example:
```
class { 'puppet::master':
  storeconfigs    => false,
  dns_alt_names   => ['puppet.example.com', 'puppet.example.org'],
}
```