Title: #247: Subdomain inherit
since this PR appears quite stalled, I'm going to close it. I still think the work is
something that SSSD would benefit from, but the work shouldn't be tracked in a PR,
unless there is active interest in merging the code.
Please let me know if I can help with resolving whatever is blocked with the PR.
See the full comment at https://github.com/SSSD/sssd/pull/247#issuecomment-390783093