Fix namespace collision

On subsequent runs after a puppetmaster restart I was seeing:

 Error: Could not retrieve catalog from remote server: Error 400 on SERVER: undefined method `[]' for Puppet::Parser::Util::Hash:Class at /etc/puppet/env/common/module/riak/manifests/appconfig.pp:36 on node $node.$domain

Appeared to be caused by a collision with the Hash class in Puppet::Parser::Util::InstanceMethods.