Title: #265: Test for issue #3391 (sss_override doesn't work with files provider)
This patch includes the test for overriden user using files provider and it's expected
to fail till we have a fix for issue #3391.
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/265/head:pr265
git checkout pr265