Title: #390: NSS: Add option to disable memcache
I changed the tests, because as they were written before they did not work (we probably
have a bug in memcache, but it is not related to these patches, because it is reproducible
even without them).
I will open a new issue to track that bug. So far it was only reproducible in the pytest
The code itself is the same, only the tests have been updated to work around the mentioned
See the full comment at https://github.com/SSSD/sssd/pull/390#issuecomment-334452440