Adds rails-controller-testing to ui-classic

This should be the only repo that needs this when running tests, so
maintaining this here means that only this repo requires it as a
dependency, not every repo that uses `ManageIQ/manageiq` in it for
testing.

manageiq-ui-classic.gemspec

@@ -34,6 +34,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency "codeclimate-test-reporter", "~> 1.0.0"
   s.add_development_dependency "guard-rspec", '~> 4.7.3'
+  s.add_development_dependency "rails-controller-testing", '~> 1.0.2'
   s.add_development_dependency "simplecov"
 
   # core because jasmine has < 3.0, not < 2.6