Fixes #8210 - Adding caching for smart-proxy puppet classes using Stefan Julin's implementation of cache

That doesn't sound right -- depending on whether cache is used Proxy::Puppet::ClassScanner will return two or four classes (see https://github.com/theforeman/smart-proxy/pull/236/files#diff-c81c1889c5ab9d5f600d7c22c4f43e5bR157)?