Switch from `login` to `username`
Switch from `login` to `username`

As per cakephp/cakephp#4861
ojengwa/cake-appengine,QoboLtd/project-template-cakephp,QoboLtd/project-template-cakephp,makallio85/fish-diary,QoboLtd/project-template-cakephp,makallio85/fish-diary,QoboLtd/project-template-cakephp,makallio85/fish-diary,ojengwa/cake-appengine,QoboLtd/project-template-cakephp