Bug #3920: Prevent 500 ScopedSearch errors on the API

This PR applies a filter on every controller, around the index action.

It's functionality is basically to avoid 500 errors caused by broken
ScopedSearch queries, for instance "wrongfield = dlkas". 

Tests just check that the appropriate template is rendered for the API, and in the UI case it checks the flash message and an appropriate redirection.

Without this PR, wrongly formed queries will result on 500 errors from the API and the UI side. Some of the controllers already implemented a fix for this, so this functionality was extracted and applied across all controllers.

Here's a list of the controllers where this is fixed (all of them except 2):

              500: settings - fixed
                      models   - fixed
                      images   - fixed
                      architectures - fixed
                      media - fixed
                      roles - fixed
                      ptables - fixed
                      operatingsystems - fixed
                      environments - fixed
                      domains - fixed
                      common_parameters - fixed
                      subnets - fixed

              200:  compute_resources - fixed
                      reports - fixed 
                      users - fixed
                      lookup_values - fixed
                      hostgroups - fixed
                      config_templates - fixed
                      puppetclasses - fixed
                      lookup_keys - fixed
                      audits - fixed

                      fact_values
                      hosts
                      are hard to fix because of post processing after search. Error handling is done in the controller itself, not on application_controller.


              n/a:   statistics
                      dashboard
                      facts
                      about
                      compute_resources_vms
                       

http://projects.theforeman.org/issues/3920