App install fails when update manager module is disabled.

If you disable update module (i.e. during install) then trying to later install an app will fail as follows:

An AJAX HTTP error occurred. HTTP Result Code: 200 Debugging information follows. Path: /batch?id=5&op=do StatusText: OK ResponseText: Fatal error: Call to undefined function _update_manager_cache_directory() in /vagrant/public/openpublic.dev/modules/update/update.manager.inc on line 812