Show private subgroups if member of parent group

What does this MR do?

If the user is member of one of the parent groups, also private groups should be shown.

Why was this MR needed?

regression introduced by https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2096/ .

It uses the changes in gitlab-org/gitlab-ce!10885.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closed gitlab-org/gitlab-ce#32135

Implementation for %9.3, because gitlab-org/gitlab-ce!11773 takes care of %9.2 .