Description of problem:
Unable to create a bookmark from search of Content credential via WebUI, 'Controller katello_content_credentials is not a valid controller' is shown in logs.

Version-Release number of selected component (if applicable):
Sat 6.4 Snap 25

How reproducible:
Always

Steps to Reproduce:
1. Navigate to Content -> Content Credentials
2. Select 'Bookmark this search' from searchbox' dropdown actions list
3. Type any bookmark name and query, press 'Save' button

Actual results:
Nothing happens, no flash notifications, bookmark was not created. Browser's console contains following line:
POST https://hostname/api/v2/bookmarks 422 (Unprocessable Entity)

production.log contains following lines:
2018-10-12T08:37:41 [I|app|] Started POST "/api/v2/bookmarks" for 10.36.117.161 at 2018-10-12 08:37:41 -0400
2018-10-12T08:37:41 [I|app|3cf22] Processing by Api::V2::BookmarksController#create as JSON
2018-10-12T08:37:41 [I|app|3cf22]   Parameters: {"name"=>"test", "query"=>"1111", "public"=>true, "apiv"=>"v2", "bookmark"=>{"name"=>"test", "query"=>"1111", "controller"=>"api/v2/bookmarks", "public"=>true}}
2018-10-12T08:37:41 [I|app|3cf22] Current user: admin (administrator)
2018-10-12T08:37:41 [E|app|3cf22] Unprocessable entity Bookmark (id: new):
  Controller katello_content_credentials is not a valid controller

2018-10-12T08:37:41 [I|app|3cf22]   Rendering api/v2/errors/unprocessable_entity.json.rabl within api/v2/layouts/error_layout
2018-10-12T08:37:41 [I|app|3cf22]   Rendered api/v2/errors/unprocessable_entity.json.rabl within api/v2/layouts/error_layout (1.7ms)
2018-10-12T08:37:41 [I|app|3cf22] Completed 422 Unprocessable Entity in 40ms (Views: 4.2ms | ActiveRecord: 6.4ms)

Expected results:
No errors, bookmark was successfully created, appropriate success message is shown.

Additional info: