fixes #6696 - API v2 - specify the key in which parameters would be wrapped rather than passing model name

specify `:host` as key rather than passing class name `Host::Base` which was incorrectly resolved to `params[:base]`
@domcleal, I think this PR can be merged to get this fix it in for `wrap_parameters :host` so it doesn't resolve to `params[:base]'. I will create another PR to add `wrap_parameters` to the other controllers to ensure that unwrap PUT/POST params even though it wont be documented.