Trigger refreshing of permissions in a migration

This migration resets `users.authorized_projects_populated` (in batches)
so that active users' permissions are refreshed on the next request.
This ensures that their permissions are properly stored.

changelogs/unreleased/refresh-permissions-recent-users.yml

+---
+title: Reset users.authorized_projects_populated to automatically refresh user permissions
+merge_request:
+author:

db/post_migrate/20170131214021_reset_users_authorized_projects_populated.rb

+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class ResetUsersAuthorizedProjectsPopulated < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  disable_ddl_transaction!
+
+  def up
+    # This ensures we don't lock all users for the duration of the migration.
+    update_column_in_batches(:users, :authorized_projects_populated, nil)
+  end
+
+  def down
+    # noop
+  end
+end