spec and fix for fogbugz lonely user problem

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/14766

I encountered this issue while manually testing all import types for
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3066

This is really due to a horrible API

```
{ 'people' => { 'person' => array_of_people_or_single_person_as_hash } }
```

See merge request !3457