Hide for instance statistics by default

Changing the default in a new migration and updating the existing
values to change the defaults for instances already exposing the statistics.

db/migrate/20180806094307_change_instance_stats_visibility_default.rb

+# frozen_string_literal: true
+
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class ChangeInstanceStatsVisibilityDefault < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    change_column_default :application_settings,
+                          :instance_statistics_visibility_private,
+                          true
+    ApplicationSetting.update_all(instance_statistics_visibility_private: true)
+  end
+
+  def down
+    change_column_default :application_settings,
+                          :instance_statistics_visibility_private,
+                          false
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20180726172057) do
+ActiveRecord::Schema.define(version: 20180806094307) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -168,7 +168,7 @@ ActiveRecord::Schema.define(version: 20180726172057) do
     t.boolean "enforce_terms", default: false
     t.boolean "mirror_available", default: true, null: false
     t.boolean "hide_third_party_offers", default: false, null: false
-    t.boolean "instance_statistics_visibility_private", default: false, null: false
+    t.boolean "instance_statistics_visibility_private", default: true, null: false
   end
 
   create_table "audit_events", force: :cascade do |t|