[katello-devel] Remiving Exception hiding from UI controllers

[Petr Chalupa]

I'm about to merge https://github.com/Katello/katello/pull/2427. I need 
some ACKs form somebody more familiar with UI. It modifies the behavior 
of how exceptions are handled. Exceptions are no longer hidden in 
development and test environment, which makes spotting problems and 
debugging much more easier.

Anonymous exceptions should not be used in controller actions, e.g.

     raise 'missing param ...' unless params[:'...']

they would generate 500 status. There is `render_bad_parameters` instead 
for this case:

     unless params[:'...']
       return render_bad_parameters 'missing param ...'
     end

will generate 400 and will show proper warning to user. see usage [1]

This PR is also fixing about 30 false positive tests and adding gem 
justified to show exception causes.

[1] 
https://github.com/pitr-ch/katello/blob/5ccbe80fff616cbb0d5af887d361e8f2e636be91/app/controllers/application_controller.rb#L360-L372