Editing a Rackspace compute resource with invalid credentials fails to load the form:

2016-11-15T10:22:06 68910d09 [app] [I] Started GET "/compute_resources/9-rackspace/edit" for 127.0.0.1 at 2016-11-15 10:22:06 +0000
2016-11-15T10:22:06 68910d09 [app] [I] Processing by ComputeResourcesController#edit as HTML
2016-11-15T10:22:06 68910d09 [app] [I]   Parameters: {"id"=>"9-rackspace"}
2016-11-15T10:22:06 68910d09 [sql] [D]   ActiveRecord::SessionStore::Session Load (0.1ms)  SELECT  "sessions".* FROM "sessions" WHERE "sessions"."session_id" = ?  ORDER BY "sessions"."id" ASC LIMIT 1  [["session_id", "68910d097bfa2184b883be61208c41ae"]]
2016-11-15T10:22:06 68910d09 [sql] [D]   User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 24]]
2016-11-15T10:22:06 68910d09 [app] [D] Setting current user thread-local variable to admin
2016-11-15T10:22:06 68910d09 [sql] [D]   AuthSource Load (0.1ms)  SELECT  "auth_sources".* FROM "auth_sources" WHERE "auth_sources"."id" = ? LIMIT 1  [["id", 1]]
2016-11-15T10:22:06 68910d09 [sql] [D]    (0.1ms)  SELECT COUNT(*) FROM "compute_resources" 
2016-11-15T10:22:06 68910d09 [sql] [D]   ComputeResource Load (0.0ms)  SELECT  "compute_resources".* FROM "compute_resources" WHERE "compute_resources"."id" = ?  ORDER BY compute_resources.name LIMIT 1  [["id", 9]]
2016-11-15T10:22:06 68910d09 [sql] [I] Successfully decrypted field for Foreman::Model::Rackspace rackspace
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered compute_resources/form/_rackspace.html.erb (1611.9ms)
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered compute_resources/_form.html.erb (1621.2ms)
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered compute_resources/edit.html.erb within layouts/application (1624.6ms)
2016-11-15T10:22:08 68910d09 [app] [I] Completed 500 Internal Server Error in 1631ms (ActiveRecord: 0.3ms)
2016-11-15T10:22:08 68910d09 [app] [F] 
 | ActionView::Template::Error ([HTTP 403 | ] Expected([200, 203]) <=> Actual(403 Forbidden)
 | excon.error.response
 |   :body          => "" 
 |   :cookies       => [
 |   ]
 |   :headers       => {
 |     "Content-Length" => "0" 
 |     "Date"           => "Tue, 15 Nov 2016 10:22:08 GMT" 
 |     "Server"         => "Jetty(9.2.z-SNAPSHOT)" 
 |     "Via"            => "1.1 Repose (Repose/7.1.5.1)" 
 |     "x-trans-id"     => "18d6fb61-5c61-4c5c-b38f-c7dcb5ee0172" 
 |   }
 |   :host          => "dfw.servers.api.rackspacecloud.com" 
 |   :local_address => "192.168.0.104" 
 |   :local_port    => 42686
 |   :path          => "/v2/10034898/flavors/detail" 
 |   :port          => 443
 |   :reason_phrase => "Forbidden" 
 |   :remote_ip     => "72.32.168.196" 
 |   :status        => 403
 |   :status_line   => "HTTP/1.1 403 Forbidden\r\n" 
 | ):
 |     3: <%= password_f f, :password, :label => _("API Key"), :unset => unset_password? %>
 |     4: <% flavors = f.object.flavors rescue [] %>
 |     5: <%= selectable_f(f, :region, f.object.regions, {}, {:label => _('Region'),
 |     6:                  :help_inline_permanent => test_connection_button_f(f, !flavors.empty?) }) %>
 |   app/views/compute_resources/form/_rackspace.html.erb:6:in `_app_views_compute_resources_form__rackspace_html_erb___4599927241175676408_70263517790060'
 |   app/views/compute_resources/_form.html.erb:22:in `block in _app_views_compute_resources__form_html_erb___2004448844999184112_70263610797940'
 |   app/helpers/form_helper.rb:280:in `form_for'
 |   app/views/compute_resources/_form.html.erb:2:in `_app_views_compute_resources__form_html_erb___2004448844999184112_70263610797940'
 |   app/views/compute_resources/edit.html.erb:3:in `_app_views_compute_resources_edit_html_erb__1721652852843436011_70263609402660'
 |   app/controllers/concerns/application_shared.rb:14:in `set_timezone'
 |   app/models/concerns/foreman/thread_session.rb:32:in `clear_thread'
 |   lib/middleware/catch_json_parse_errors.rb:8:in `call'
 |   lib/middleware/tagged_logging.rb:18:in `call'
 | 
 | 
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered /home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/actionpack-4.2.7.1/lib/action_dispatch/middleware/templates/rescues/_source.erb (8.3ms)
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered /home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/actionpack-4.2.7.1/lib/action_dispatch/middleware/templates/rescues/_trace.html.erb (2.9ms)
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered /home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/actionpack-4.2.7.1/lib/action_dispatch/middleware/templates/rescues/_request_and_response.html.erb (0.9ms)
2016-11-15T10:22:08 68910d09 [app] [I]   Rendered /home/dcleal/.rvm/gems/ruby-2.3.0@foreman/gems/actionpack-4.2.7.1/lib/action_dispatch/middleware/templates/rescues/template_error.html.erb within rescues/layout (28.5ms)

It looks like flavors is being lazy-loaded so the rescue isn't catching any authentication failures, so it instead fails when !flavors.empty? is checked on the line below.