set controller#action on a controller exception

closes: FOO-1157

The x-canvas-meta header is set on
`after_action :set_response_headers`
app/controllers/application_controller.rb#81 (ish).
The header is not set on an exception

This will provide more context in splunk search.

```
index="canvas_iad" source="app/canvas/prod/*/apache2/nomnom"
http_request!=*pandata_events_token* vhost!=*elb*
vhost="browardschools.instructure.com" http_status=500
```

Test plan
a) jenkins pass

Change-Id: I2ee19afb909fa8efb9c5a5bd9eec3136920d0234
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/251512
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Natarajan Santhosh <snatarajan@instructure.com>

app/controllers/application_controller.rb

@@ -1494,6 +1494,10 @@ class ApplicationController < ActionController::Base
 
   # analogous to rescue_action_without_handler from ActionPack 2.3
   def rescue_exception(exception)
+    # On exception `after_action :set_response_headers` is not called.
+    # This causes controller#action from not being set on x-canvas-meta header.
+    set_response_headers
+
     if config.consider_all_requests_local
       rescue_action_locally(exception)
     else

spec/integration/application_spec.rb

@@ -73,6 +73,15 @@ describe "site-wide" do
       expect(response[x_canvas_meta]).to match(%r{o=courses;n=show;})
     end
 
+    it "should set controller#action information in API requests on 500" do
+      course_with_teacher_logged_in
+      allow_any_instance_of(CoursesController).to receive(:index).and_raise(ArgumentError)
+      get "/api/v1/courses"
+
+      assert_status(500)
+      expect(response[x_canvas_meta]).to match(%r{o=courses;n=index;})
+    end
+
     it "should set page view information in user requests" do
       course_with_teacher_logged_in
       Setting.set('enable_page_views', 'db')