Add failing test for list data sets

The list data sets view is only going to return the data sets that the
requesting user is allowed to see unless they have the admin permission.
Only list data sets a user has access to

- If the user has the 'admin' permission show them all data sets
otherwise;
- If the user has a backdrop_user show them the data sets they have
  access to
otherwise;
- Show the user an empty list of data sets
Only show data sets a user has access to

Same rules as in 012bb2210 applied to the detail view.
Merge pull request #172 from alphagov/oauth-list-data-sets-2

OAuth permissions for data sets