Fixes #11924 - Substitute .scoped by .where(nil) to force return relation

On Rails 4 .scoped is deprecated. Calling .all on the model returns the
equivalent ActiveRecord relation object on Rails 4, but on Rails 3 it
returns an Array right away.

A proper replacement we can use is where(nil) - it's ugly but it returns...

Fixes #12089 - fix using unwrapped parameters in config templates API controller

Fixes #11921 - load dynamic features during runtime

Fixes #11237 - documenting hostgroup association to compute profile

fixes #11996 - use preload to avoid multiple fact/host table joins

When retrieving fact_values as a non-admin user, the my_facts scope
performs a join to the hosts table. The .includes(:host) also performs
a join via eager loading, and when both are combined with a scoped...

Fixes #11764 - Taxonomy parameters can be accessed through API

Fixes #11401 - Add scoped search to auth_source on name

Fixes #2267 - general rebuild of TFTP, DNS, DHCP

Refs #11693 - APIv1 returns message when attempting deletion of Smart class parameter

Fixes #3650, #11600 - Compute Resource availability_zones, flavors, security_groups API v2 endpoints