Change to default port

Just a quick change, but I might be misunderstanding whats going on.

Is there any reason you guys pick a different port for the boxen install of mongo rather than the standard 27017?

Wouldn't it be better to change the `class mongodb::config` to the default, and if the person wants their app to use a different port, change the `mongod.conf.erb`?

Thanks! :+1: