Give reporters the ability to download artifacts.

Also fix a few places where page_404 should be render_404.

app/controllers/projects/builds_controller.rb

@@ -42,7 +42,7 @@ class Projects::BuildsController < Projects::ApplicationController
 
   def retry
     unless @build.retryable?
-      return page_404
+      return render_404
     end
 
     build = Ci::Build.retry(@build)
@@ -72,7 +72,7 @@ class Projects::BuildsController < Projects::ApplicationController
 
   def authorize_manage_builds!
     unless can?(current_user, :manage_builds, project)
-      return page_404
+      return render_404
     end
   end
 end

app/controllers/projects/commit_controller.rb

@@ -79,7 +79,7 @@ class Projects::CommitController < Projects::ApplicationController
 
   def authorize_manage_builds!
     unless can?(current_user, :manage_builds, project)
-      return page_404
+      return render_404
     end
   end
 end

app/models/ability.rb

@@ -160,6 +160,7 @@ class Ability
       @project_report_rules ||= project_guest_rules + [
         :create_commit_status,
         :read_commit_statuses,
+        :read_build_artifacts,
         :download_code,
         :fork_project,
         :create_project_snippet,
@@ -175,7 +176,6 @@ class Ability
         :create_merge_request,
         :create_wiki,
         :manage_builds,
-        :read_build_artifacts,
         :push_code
       ]
     end