Title: #390: NSS: Add option to disable memcache
In retrospect I agree that we should document all options. It is not that hard to find the
options but currently it is not easy to understand the side effects to those options
because they are not documented.
Documenting them gives us the ability to explain why it is not a good idea to use them,
what the side effects are and why they are there at all.
See the full comment at https://github.com/SSSD/sssd/pull/390#issuecomment-331878234