Engine: Fixed rspec controller tests

Fixed some rspec api controller tests to work with the enginification branch.
Engine: update several controller tests to pass as engine

- updated the following controllers from spec/controllers/api/v1:
  - subscriptions
  - sync
  - sync plans
  - system group errata
  - system group packages
  - system groups
Engine: Fixed more api controller tests

Conflicts:
	app/controllers/katello/api/v1/systems_controller.rb
Engine: Made some corrections w.r.t PR 3377
Engine: Fixed a katello test runner lookup issue
Engine: Removed an unused method
Engine: Updated the test controllers based on david's comment
Engine: Addressed PR comments

Changed must_bes to 'should be' as suggested in PR 3408

Added a new line between requires and first line
as suggested in the comments for PR 3377
Engine: Fixed tests as per PR 3414
Merge pull request #3414 from parthaa/engine-spec-redux

Engine api spec tests
Engine: fixes #3730 - async-fix - re-applied change from OpenStruct to Class
Merge pull request #3418 from thomasmckay/async-fix

async-fix - re-applied change from OpenStruct to Class