fixes #4181 - API V2 return object for POST/PUT/DELETE should *not* include root node

@waldenraines, @daviddavis, I reviewed katello code and see how you are rendering RABL templates for each each action with `respond_for_#{action}`

Foreman is essentially just doing `render :json => @resource` for the response for PUT/POST/DELETE

This fix changing `resource_class.include_root_in_json = false` in Api::V2::BaseController fixes the issue without affecting V1.

In doing so, I noticed the inflection bug with "HostClass" and "HostgroupClass"

If this `before_filter` is also on the `index` actions, then several tests fail (dashboard, statistics, autosign, etc). I didn't investigate these failures as they don't affect our consistency in documentation between katello and foreman.  All tests pass with `:except => [:index]`