Bug/security ddoc

As in #8388, create-user-db script is failing to set security ddocs. I checked code and the call is incorrect, but looking correct. So, ensure_ddoc parameter is causing too much confusion and ended up causing this logic mess up. I removed it on code and on tests, making the create script work properly again. The create-user-db itself has a migration option, so no additional migration script should be required. Just run it with --migrate-all.