Set settings explicitly instead of stubbing Settings

`test/functional/smart_proxy_auth_test.rb` is failing in my plug-in because it's stubbing Settings:

    unexpected invocation: Setting(id: integer, name: string, value: text, description:
    text, category: string, settings_type: string, default: text, created_at: datetime,
    updated_at: datetime).[](:require_ssl_puppetmasters)...

It's because I'm chaining `auth_smart_proxy` and referencing a setting that's not available in the stub.