Add support for sensitive config

[teluq-pbrideau]

I use a proxy with a password in my puppet.conf, and would like it not to be displayed in the logs when the config is pushed. It would be nice for this class to support the Sensitive type.

$secret = Sensitive('mysecretpassword')
class { 'puppet':
  agent_additional_settings => {
    'http_proxy_user      => 'proxyuser',
    'http_proxy_password' => $secret,
  }
}

I’ve opened an issue on the concat module that need a change before it could be addressed on this module: puppetlabs/puppetlabs-concat#742

For now, I’ve disabled the diff completely with a default value for concat module

Concat {
  show_diff => false,
}