Make project private to avoid spam on issues

This is needed for staging env where we have Akismet for spam
detection

qa/qa/specs/features/browser_ui/2_plan/issue/mentions_spec.rb

@@ -11,6 +11,7 @@ module QA
 
         project = Resource::Project.fabricate_via_api! do |resource|
           resource.name = 'project-to-test-mention'
+          resource.visibility = 'private'
         end
         project.visit!