Fix filter published nodes

Node::filterPublishedNodes method was broken since it was created (https://github.com/croogo/croogo/commit/a397845c448465cbaa1db422217d782571f6f706).

Undefined variable for `$visibilityRoleFields`. I quickly wrote down a (basic) test to ensure method is working fine. 
Don't we need to compare against current users' role id?  Otherwise only role id = 3 can be dynamically hidden.