Change the user logout path.
function system_update_7015() {
db_update('menu_links')
->fields(array(
'link_path' => 'user/logout',
))
->condition('link_path', 'logout')
->execute();
db_update('menu_links')
->fields(array(
'router_path' => 'user/logout',
))
->condition('router_path', 'logout')
->execute();
db_update('menu_links')
->fields(array(
'menu_name' => 'user-menu',
'plid' => 0,
))
->condition(db_or()
->condition('link_path', 'user/logout')
->condition('router_path', 'user/logout'))
->condition('module', 'system')
->condition('customized', 0)
->execute();
}