[SSSD] [sssd PR#347][synchronized] Fixes related to negative cache and "root" user/group

[fidencio]

   URL: https://github.com/SSSD/sssd/pull/347
Author: fidencio
 Title: #347: Fixes related to negative cache and "root" user/group
Action: synchronized

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/347/head:pr347
git checkout pr347