Add failing feature spec detailing a maintainer creating a subgroup
Add failing feature spec detailing a maintainer creating a subgroup

- Change the two existing feature examples that create a subgroup to
  elucidate that the owner is creating the subgroup

- Nest two more specs inside the 'subgroup support' context detailing
  what happens when a maintainer attempts to add a subgroup (one with
  subgroup support, and one without)

mmkassem/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq