[SSSD] [sssd PR#558][opened] WIP: Add a test for sss_nss_getgrouplist_timeout and fix invalidating the initgroups cache

[jhrozek]

   URL: https://github.com/SSSD/sssd/pull/558
Author: jhrozek
 Title: #558: WIP: Add a test for sss_nss_getgrouplist_timeout and fix invalidating the
initgroups cache
Action: opened

PR body:
"""
This is a WIP on adding tests for the sss_nss_ex interface. I covered only the
sss_nss_getgrouplist_timeout function so far.

I'm submitting the PR already in this state to get some feedback if this
coverage is enough and the other functions can be covered similarly or
if there is some issue with this approach.

Also, I found a bug in invalidating the initgroups memory cache, that's
the first of the two patches. Here I'm really not sure if the fix is even
how the issue should be fixed, so I just hacked something up, even without
allocation checks etc.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/558/head:pr558
git checkout pr558