Include the 'also attends cabinet' ministers in the sorting

https://www.pivotaltracker.com/story/show/48560287
Test for also_attends_cabinet seniority reorder
Merge pull request #476 from alphagov/reorder-ministers-who-also-attend-cabinet

Include the 'also attends cabinet' ministers in the sorting

https://www.pivotaltracker.com/story/show/48560287